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ALM
October 31st, 2002, 06:11 PM
As you know, USMS passed a rule that will require us to measure any pool in which we hold a meet, IF we want the times from that meet to count for USMS Top Ten. I'm trying to figure out the best way to do this - what sort of tape to buy, the best method to use, etc. (Can you tell that I'm an engineer?)

I'd like to hear from those of you who have measured pools. What brand of tape do you recommend? What length? (60 meters?) Any idea where I can buy such a tape? Any suggestions for how to get a good (accurate) measurement, especially over a 50 meter course?

FYI, below are the instructions on how to perform pool measurements, taken from the USMS Pool Length Certification Form.

==================
"A completed form must be on file or submitted with an application for sanction or recognition to your LMSC Sanctions Chairman. For pools utilizing bulkheads, completed forms from each session must be included with results sent to the Top Ten Chairman if the results are to be included in Top Ten submissions.

Measurement procedures:

--Measurements must be conducted using a measuring device with the minimum measuring quality of at least ± 0.005 m (±.0.20 inches or 0.016 feet) over the nominal distance. A laser based measuring device may be used but it must be as accurate as required for steel tapes. Tapes may not be combined to perform the measurements.

--Measurements may be reported in either the English system (feet/inches) or the metric system (meters/centimeters).

Instructions for pool length measurements:

--Measurements must be conducted for each lane. Inspect each end of the pool to insure that it is vertical. If there are any protrusions from the wall into the pool between 0.8 meters (2.5 feet) below the surface to the top of the touch pad or wall or up to 0.3 meters above the surface whichever is higher, you must use the protrusion as your measurement point. Otherwise, measurements must be taken in the center of each lane at water level.

--The measuring device shall be moved up/down and left/right at least 12 inches (unless you are on a protrusion) during each measurement and the minimum distance for each measurement recorded.

--Measurements may be conducted with or without touchpads in place. However, if touchpads are used the pool must still meet the length requirements with them in place.

--Permanent courses need only be measured once unless structural changes have occurred since original measurement.

--For pools with a moveable bulkhead, after each session a course measurement must be confirmed by a responsible person. Only the outside lanes and a single center lane need to be measured to confirm the integrity of the bulkhead and its placement."

MPohlmann
November 2nd, 2002, 01:37 PM
Hi, Anna Lea,

We are so fortunate to have a School of Engineering at Southern Illinois University. I consulted with the professor who teaches surveying. He and his students will be measuring our 50 meter X 25 yard pool next month. I also asked his advice concerning measurement using a tape for those who were not so fortunate as to have free surveyors. I shared this information with Pieter Cath and these guidelines will be included in the LMSC handbook. Also, the directions on the final revision of the Pool Certification form are a bit simpler than those you listed in your message.

GUIDELINES FOR POOL MEASUREMENT

The 2003 USMS Rules provide that results from events conducted in pools that do not meet the minimum pool length requirement (minus 0.00M) shall not be acceptable for Record Applications or Top Ten submissions. All competition pools shall be measured in each lane. In measuring your pool, the goal is to meet the minimum length requirement. Your pool should not be shorter than 50.00 meters (164 ft, 1/2 inch) for long course; 25.00 meters (82 feet, 1/4 inch) for short course meters; and 25.00 yards (75 feet) for short course yards. Pool certification shall be reported on the USMS pool certification form. Certification data need only be filed once unless structural changes have occurred since original certification. If your pool has a moveable bulkhead, you must have an initial pool certification on file for each lane. In addition, for pools with moveable bulkheads, course measurement of the two outside lanes and a middle lane must be confirmed at the conclusion of the session (each day of the meet).

HOW TO COMPLY:

First check with your LMSC or the USA Swimming LSC to see if a pool certification is already on file. If so, check that the measurement was done with a steel tape or electronic distance measuring device. Fiberglass tape is not acceptable. Also check to see that each lane was measured.

Electronic measurements are superior to tape measuring techniques. The services of a professional land surveyor may be your best choice. Check with the Civil Engineering department of your local university. They may be willing to do your pool measurement as a project for surveying students. Some community colleges also offer surveying classes. Each state has a State Professional Land Surveyors Association which maybe able to provide free or inexpensive services to your non-profit organization. Perhaps you have such equipment already on hand and know how to use it properly. If so, you need to be aware of the tolerance levels of your equipment over the distances required. It must be accurate to the 1/100th of a meter (1 cm). To achieve this accuracy, the markings on the tape must be to the millimeter, thousandth of a foot, or eighth of an inch. There are handheld laser devices available, priced around $500, that can measure over these distances with accuracy to the millimeter.

If you must measure with a tape, use a steel tape longer than the distance to be measured. Typically, this would be a 200 ft tape for 50 meter pools and 100 ft tape for 25 yard or 25 meter pools. Be attentive to the markings of the tape. Some are marked in tenths of a foot, others in feet and inches, others in meters. Fiberglass tapes are not permitted.

The tape should be supported at the same elevation every 20 ft. to prevent sag. This can be accomplished using kickboards, support poles, or threading the tape through pull-buoys. Thus for a 50 meter pool you should have at least 9 kickboards. Be sure that your tape is taut. Unsupported tape over 50 meters will require about 44 pounds of tension to eliminate sag, 30 pounds over 25 yards/meters. The tension can be determined using a tension handle attachment to the tape.

Measure your pool with touchpads in place if they are generally used in competition. Have touchpads at each end of the pool if that is your usual configuration. Note on the certification form whether touchpads were in place for the measurement and how many were present per lane. Most touchpads have a thickness of 8 mm (.008 meters) but could extend out further in the pool if they are not flush with the wall.

If a visual inspection indicates irregularities in the wall of the pool, one can use a waterproof vertical level of the appropriate length (80 cm minimum) to make sure the wall is vertical. If the level cannot be submerged, one can fasten a yardstick or other device to the level in order to reach the required depth. Only if the walls bow inward toward the pool would an actual measurement be necessary.

ALM
November 2nd, 2002, 05:51 PM
Mary,

You state that the tape must have an accuracy of 1/100th of a meter (0.010m) over the distance measured (I'm assuming 50 meters). The pool certification form that I quoted stated that the tape's accuracy must be 0.005m. That's twice the accuracy of 0.010m.

Did your figure, 0.010m, come from Pieter Cath?

The reason I ask is that usually the price of the measuring device goes up as the guaranteed level of accuracy goes up. In our case, we're going to have to purchase a tape because one of our pools has a movable bulkhead.

MPohlmann
November 2nd, 2002, 07:01 PM
Hi, again, Anna Lea,

New Rule 105.1.5 states:

"Results from events conducted in pools that do not meet the minimum pool length requirement (minus 0.00M) shall not be acceptable for Record Applications or Top Ten submissions."

In an earlier draft of our Guidelines for Pool Measurement, we had this wording:

"Your pool should not be shorter than 49.995 meters (164 ft, 1/2 inch) for long course; 24.995 meters (82 feet, 1/4 inch) for short course meters; and 24.995 yards (74 feet, 11 7/8 inch) for short course yards."

Pieter asked for the above wording, but then he changed back to the 50.00 meters, 25.00 yards in the final version of the Guidelines in an attempt to avoid confusion. Nonetheless, he agrees that the earlier wording is more precisely correct and coincides more closely to the directions on the Pool Certification form.

At any rate, the following information regarding the accuracy of the tape is still in the Guidelines and should help in deciding the quality of tape to purchase:

"To achieve this accuracy, the markings on the tape must be to the millimeter, thousandth of a foot, or eighth of an inch. "

michaelmoore
November 2nd, 2002, 09:50 PM
I have a couple of concerns here.

When measuring the pool, one has to allow for touch pads (as stated in the instructions). If you never plan to have touch pads, there is no problem. If you are going to have touch pads, then you either take your measurement with the touch pads in, or you allow for them in your calculation. For long course pools, sometimes touch pads are put in both ends of the pool. ( I would also suggest that this is also important with pools that have bulkheads). If you are fortunate enough to have supervised students from an engineering class, they may forget to take that into consideration.

There are handheld laser devices available, priced around $500, that can measure over these distances with accuracy to the millimeter.

Mary, would you let us know where these devices can be purchased, in the past we have seen laser measuring devices with this accuracy costing more than $5,000. Electonic pricing is always coming down, so devices this accurate may be available. If they are, I think we would like to purchase one.

If any measurement is very close, ie about 50.03 meters, and the measurement is made with a metal tape, remember that the tape was probabily calibrated to a measurement made at 20 Deg C. If the temperature is warmer (or cooler), you may have to calculate the length after including the co-efficient of expansion.

michael

MPohlmann
November 2nd, 2002, 10:34 PM
Hello, Michael,

We plan to measure our pool with touchpads in place at both ends of the 50 meter pool because that is the configuration that we generally use for long course. If we find the pool is too short, we will measure with touchpads at just one end and discontinue our practice of using touchpads at both ends. World records have been set at our facility and the previous measurements seem to have given us sufficient space for two 8 mm touchpads. We'll see.

While I don't want to promote any particular brand of laser apparatus, an Internet search produced this Canadian website for a LEICA Disto Lite Laser Distance Measurer which is said to be accurate to the millimeter at the distances we require:
http://www.deakin.com/product.cfm?ProductID=1403
Aprox. US Price:***$449.08

This product was also shown at the following US website, but no price was listed.
http://www.forestry-suppliers.com/product_pages/View_Catalog_Page.asp?ID=5717

With regard to the coefficient of expansion, an earlier draft of the Guidelines for Pool Measurement included the following information.

"Steel tapes are standardized at 68 degrees Fahrenheit. The coefficient of expansion on most steel tapes is .0000065 ft per ft and average 0.01ft every 15 degrees over a 100 ft distance. If your water/air temperature were around 83 degrees, you would experience a stretch of your tape of 0.01 ft using a 100 ft tape or 0.02 ft with a 200 ft tape. Thus your pool may appear to be shorter than it really is. Record the measurement without correction for temperature. Also record the temperature. Only if your pool measurement comes up short would the temperature factor need to be considered."

We felt this too technical to include in the final version, since the stretch of the tape at higher than the 68 degree standard would not have much impact. The greatest source of measurement error with a tape is sag.

Hope this is helpful.

michaelmoore
November 2nd, 2002, 11:05 PM
While I don't want to promote any particular brand of laser apparatus, an Internet search produced this Canadian website for a LEICA Disto Lite Laser Distance Measurer which is said to be accurate to the millimeter at the distances we require:
http://www.deakin.com/product.cfm?ProductID=1403
Aprox. US Price:***$449.08

from that page:

DISTO™ lite is a one-person operated unit, measuring distances from 0.3m to over 100m. Measure areas and volumes comfortably and quickly with ±3 millimeter accuracy, even in difficult or unreachable places.

This product was also shown at the following US website, but no price was listed.
http://www.forestry-suppliers.com/product_pages/View_Catalog_Page.asp?ID=5717

From that page

Designed for fast, accurate and efficient measurements, from 1" to over 330" with ±1/8" accuracy!

1/8" equates to a little more than 3mm.

I think the tolerance has to be less than 0.5mm.

I was hoping for an inexpensive laser measuring device that will meet specs. Maybe it is out there.

World records have been set at our facility and the previous measurements seem to have given us sufficient space for two 8 mm touchpads. We'll see.


If world records havebeen set at your facility, it should have already been measured. I don't think your pool has to be remeasured unless it has undergone reconstruction or you are using a bulkhead.


michael

Phil Arcuni
November 3rd, 2002, 01:17 AM
I can't tell you the *pride* I feel reading this thread!

MPohlmann
November 3rd, 2002, 06:59 AM
Hi, Michael,


I think the tolerance has to be less than 0.5mm

I believe the tolerance required is less than 5 mm = 0.005m, approximately 1/8 inch. You're not going to get better than 1/8 inch tolerance using a steel tape and the human eye, either.


If world records havebeen set at your facility, it should have already been measured. I don't think your pool has to be remeasured unless it has undergone reconstruction or you are using a bulkhead.

Yes, our pool has been measured in the two outside lanes and center lane which was all that was required prior to January, 2003. Now we must measure all lanes, which we will do using an electronic distance measuring instrument (infrared) on December 16th, courtesy of the Southern Illinois University department of Civil Engineering.

michaelmoore
November 4th, 2002, 01:50 AM
Mary:

You are correct on the .005 distance. Sometime I am going to get the dimensions straight between centemeters and millimeters. (of course my favorite dimensions is furlongs per fortenight - but that is in the English system).

But being a gluton for punishment, lets revisit the co-efficent of expansion for a moment.

"Steel tapes are standardized at 68 degrees Fahrenheit. The coefficient of expansion on most steel tapes is .0000065 ft per ft and average 0.01ft every 15 degrees over a 100 ft distance. If your water/air temperature were around 83 degrees, you would experience a stretch of your tape of 0.01 ft using a 100 ft tape or 0.02 ft with a 200 ft tape. Thus your pool may appear to be shorter than it really is. Record the measurement without correction for temperature. Also record the temperature. Only if your pool measurement comes up short would the temperature factor need to be considered."

We felt this too technical to include in the final version, since the stretch of the tape at higher than the 68 degree standard would not have much impact. The greatest source of measurement error with a tape is sag. "

Lets assume as your example the temperature is 83F, then the tape would expand about 5 mm. If you already have a tape that is 5 mm long (the degree of uncerntainty of tape and still meeting spec at that length- this would be on the long side) your 50.00 M pool will measure out at 49.99 (it fails).

If I am thinking correctly (and there is no guarantee about that), sag would introduce an error that would make the pool appear to be longer than it is.

In a thread on the USMS forum titled "The Losers" on page 4 of discussion, I wrote about trying to calculate the true length when there is sag.

"Rob Copeland wrote back "a true 25 meter pool is measured with a 0.1 meter sag (about 4 inches), in the tap, the length on the tape would read 25.001066663 meters"

According to Rob, the formula used to calculate the segment of a parabola is
s = sqrt[4h2+c2/4]+[c2/(8h)]* ln[(2h+sqrt[4h2+c2/4])/(c/2)]
Where: s = tape distance, h = midpoint sag and c = true pool length."

To me it appears that the sag introduces less error than expansion, but the errors are going the other way from the coefficient of expansion. (co-efficent of expansion errors make the pool appear shorter than it is (if the temperature is warmer than 20C.) sag errors make the pool appear longer than it is. It might be that the errors cancel out each other. I should also say that my head hurts when looking at the equation and I did not recalculate Robs findings (so if I am wrong, I am blaming Rob).

I think in the final analysis, there are going to very few pools that are going to come so close to the 50.00M min length. However, I would think that it would be good if we asked for the ambiant temperature when the people make their length measurement (as you seem to suggest), so that we can recalculate a pool that is short by 1-2cm. This may only affect one or two pools in the country, but better to have pools where we can legitimately swim for records than not have them because of bad measuring protocols.

To change the subject a little

I have not seen seen us provide guidence on the setting up of a pool with a bulkhead. The distance should be measured before the meet begins and it must be measured at the end of each day.

If someone is setting up a 50 M pool that has a bulkhead and two standard 8mm touch pads (pads at each end), the pool is being measured with a laser that has a 3mm + or - . What should be the distance from the edge of the pool to the beginning of the bulkhead?

I would suggest the distance should be 50.19M. This allows for both pad (0.16M) plus the measurement error. just a thought

michael

Phil Arcuni
November 4th, 2002, 11:05 AM
I have heard of a couple of cases where tightening the lane lines cause the bulkhead to bow, making the pool too short, especially in the center lanes. If the bulkhead tends to do that, the pool should be measured after the lane lines are installed, every time.

NASTISWMR
November 4th, 2002, 01:20 PM
Anna Lea:

We purchased a steel tape with nyon coating (won't rust) at Lowe's. If my memeory is correct we paid less than $30. It is a 200' tape I think.

Worked quite well.

ALM
November 4th, 2002, 03:53 PM
Thanks, NASTISWMR - I'll check out Lowe's or Home Depot first. $30.00 sounds like a bargain. (By the way, who are you? You must be either Doug, Melissa, Cheryl, or Dick?)

Phil, the new rule states that a pool with a movable bulkhead must be measured at the beginning of the meet and again at the conclusion of the meet, just in case someone tightens the lane lines during the meet.

Phil Arcuni
November 4th, 2002, 05:43 PM
Thanks Anna, I knew that . . . :o

Michael - The pool will contract and expand with temperature also. I do not know if it will expand or contract at the same rate as the tape, however. Anyway, if the pool water is maintained at competition temperature (and the tape in or on the water) it should not be affected by temperature too much. The measurements should really be done with the pool full (is that required?) because the pool will be a different length if the pool is full of water, than when it is not. This would be particularly true for deep pools.

It is good that the rules specify a length and a way to measure it. Suppose you measured you pool to be 50.000 - 0.000 m following the rules with a steel tape with 0.005 resolution. Then someone else come along with a super-duper laser system with a 0.001 m resolution, and measures the pool to be 50.998 m. No conflict - the second system has a better resolution and the measurements are consistent. Is the pool still legal? You bet, because the method of measurement is defined.

That is why this question, how to measure the length? while geeky, is still important.

ljlete
November 7th, 2002, 08:59 PM
For reasons that should be obvious, I need to not comment about most of what goes on here because one never know when one would be asked to intervene or interpret but I felt a story here was useful.

For a number of years now, I have been officiating at the USA-S Sectional meet that one and now both of my daughters have been competing. A couple of years ago, I was pulling duty as the turn judge at the turn end during the 1000 Free on the first night of the meet. The meet was being conducted in a 50 meter pool with two bulkheads set at 25 yards. I sat down on the corner of the pool and looked down to watch the turns and quickly noticed that the bulkhead was far from being straight. In fact the bow in the center of the pool was on the order of 4-5 inches! (In the 1000 that amounts to over 13 feet difference.) At the time I was not one of the assigned crew, so I got the attention of one of them and explained what I saw. Now at least half of the event had already been contested. No one did anything and I didn't push it that night.

The next morning, I went up to the Meet Referee and simply said "You have a problem". After he said "I do?", I brought him over and showed him the bulkhead. We then scrambled to do what we could. The first thing that happened was the double lane lines were reduced to single lane line that were only as tight as they needed to be. That took care of about half of the buldge. Prelims were run in that configuration. Between prelims and finals, the maintenance crew came in with two come-alongs, broke open the back of the bulkhead and pulled the two bulkheads together in order to straighten the competitive one. The meet then proceeded with what was close to a regulation course. Things like this happen and to this day, I wonder how many NCAA cuts were made in the center lanes of that pool.

rseltzer
June 25th, 2003, 01:38 PM
This subject is aptly titled.

We have been discussing the "art" of pool length certification. After measuring a 25 yard course with steel tape measure it became obvious to all involved that a laser device has several advantages (accuracy, speed, etc). It's also pretty hard to imagine measuring a 50 meter pool with a 200 foot steel tape and keeping it tight even and just on top of the water so that the measure is accurate.

So, NEM is seriously considering purchasing a laser device. One NEM found a:
The DISTO Pro4a. Specs says it is +/- 1.5mm. The USMS rules allow for
+/- 0.005 m which is 5 mm. $725. Others seem available within the allowable tolerance for a few hundred dollars less but we are inclined to get the slightly more expensive one.

Another NEM wondered how one mounts both the laser and "target" such that they are directly above the wall.

We strongly suspect that others out there have experience with laser devices and this might be of general interest as we come into the LCM season and I can't imagine many of you meet directors are relishing the idea of measuring a LCM pool with a steel tape.

Any experience with laser measuring devices and how to use them properly?

old dog
May 17th, 2004, 08:33 PM
more

breastroker
May 19th, 2004, 12:48 AM
SPMA discussed this with a mechanical engineer who knew about laser measurements, and they quickly added that measurement over water was impossible. Reflections from the water supposedly ruin the accuracy. I have not looked at the laser device web sites listed, do they mention measurement directly over water?

The engineer added we should use a surveyor, only $300-$500 per pool.

SPMA has used a special steel tape that uses a tension device to determine droop and maintain accuracy. The tape is over 20 years old, and very high quality. I guess we got our monies worth out of it:p

Conniekat8
May 19th, 2004, 01:59 PM
Originally posted by breastroker
SPMA discussed this with a mechanical engineer who knew about laser measurements, and they quickly added that measurement over water was impossible. Reflections from the water supposedly ruin the accuracy. I have not looked at the laser device web sites listed, do they mention measurement directly over water?

The engineer added we should use a surveyor, only $300-$500 per pool.

SPMA has used a special steel tape that uses a tension device to determine droop and maintain accuracy. The tape is over 20 years old, and very high quality. I guess we got our monies worth out of it:p

Hi Wayne,
I'll have to talk to you and Steve about this in private....
Actually, I already started dialoging with Steve about this... :)

ljlete
May 19th, 2004, 02:23 PM
Wayne,

I am curious as to the physics behind the inability of a laser to measure over water. The laser is a parallel beam of light with very little divergence, especially over the distances we are talking about. Therefore, there should be no reflection off of the water. At least this should be the case with the beam going from the laser to the other end. Now, maybe there is a problem if the target causes the beam to diffuse but given that the instrument averages multiple measurements and the water is not likely to be still (to the same degree as the beam is coherent) then the noise should average out. Did he/she give you an explanation?

Leo

Conniekat8
May 19th, 2004, 02:46 PM
Originally posted by ljlete
Wayne,

I am curious as to the physics behind the inability of a laser to measure over water. The laser is a parallel beam of light with very little divergence, especially over the distances we are talking about. Therefore, there should be no reflection off of the water. At least this should be the case with the beam going from the laser to the other end. Now, maybe there is a problem if the target causes the beam to diffuse but given that the instrument averages multiple measurements and the water is not likely to be still (to the same degree as the beam is coherent) then the noise should average out. Did he/she give you an explanation?

Leo

I'll look up the technical details, I had read them about 3 years ago when my company was looking into purchasing the reflectorless laser surveying equipement.
It has to do with the way water reflects the dipersed signal, and the feedback you get to the instrument gets a 'dirty' signal back, and you can never be very certain oif the signal you read back is from the target you sighted, or from the interference.
When you get into higher precision measurements, these details matter.
If you were measuring something to +/- few inches, it wouldn't be that critical. This is just why there is a lot of laser instrumentation used in grading, because the accuracy needed is often in inches, and not thenth's of an inch, and when you need to build hardscape and buildiongs and higher precision things, surveyors come in with higher end instrumentation, which is not 'laser' based... Even though coloquially, many people tend to call instruments we surveyors use "Lasers", they're not lasers.

I'll look up the technical details and specs that come with the laser instruments, it's all written and explained in there. I just don't recall all of it off the top of my head.

mattson
May 19th, 2004, 04:22 PM
I don't know anything about these laser sighters, but I do know a little physics. The speed of light depends on the medium it passes through (air, glass, water, etc.). This will cause all sorts of interesting phenomena. Think of a mirage on a hot day. :cool: So it sounds like the argument is that the optical properties of the layer of air just above a body of water are different enough than the surrounding air (due to temp, humidity, etc.), that it can throw off these instruments.

Or maybe I'm barking up the wrong tree. :)

(Connie, how would you get a more accurate distance measurement? You mentioned higher-end non-laser based instruments. I ask, because the definition of a "meter" used to be a physical bar of platinum stored somewhere, and is now based on a wavelength of light.)

Conniekat8
May 19th, 2004, 05:30 PM
Originally posted by mattson
I don't know anything about these laser sighters, but I do know a little physics. The speed of light depends on the medium it passes through (air, glass, water, etc.). This will cause all sorts of interesting phenomena. Think of a mirage on a hot day. :cool: So it sounds like the argument is that the optical properties of the layer of air just above a body of water are different enough than the surrounding air (due to temp, humidity, etc.), that it can throw off these instruments.

Or maybe I'm barking up the wrong tree. :)


You're right, and you're preaching to the quire, at least as far as I'm concerned. It's not so much the properties of the layer above the water, but it's the fact that it's being sughted to a non-perfect target. You're trying to reflet the laser beam ioff an uneven wet surface, which is also just inches from water.

I still haven't had the time to pull out the papers that talk about the issues with laser sighting near water and on wet surfaces. I do know that when I looked into it 3 years ago when considering a purchase of a refined piece of equipement, it made it non precise enough for cetain applications, that were near water, and would not work well when the sigted surface was wet...
That' when it comes to the 'visible laser beam measurements'


Originally posted by mattson

(Connie, how would you get a more accurate distance measurement? You mentioned higher-end non-laser based instruments. I ask, because the definition of a "meter" used to be a physical bar of platinum stored somewhere, and is now based on a wavelength of light.)

The original definition of a meter was astronomically based. It was the 1/10,000 of the 1/4 of the length of the central meridian.
To generalize it is based on the earths circumference, measured along the central meridian.

The bar that was cast to that distance... it's length was based on the astronomical observations.
Later on it got redefined to the specific period of the wavelength of light.

ljlete
May 19th, 2004, 06:04 PM
Unfortunately, this discussion is split between two threads. So to answer questions on both:

The reality of what we are trying to do is that we cannot build pools that are either precise or accurate enough to say that the difference in time that we measure (0.01 second) is meaningful (if we assume the USA-S maximum length of +0.03 meters) for anything other than a sub 20-second 50-yard freestyle. So given that, what do we do? The best we can or get faster :) I have done the math and actually wrote a white paper that we used in our discussions about this issue. Part of the problem is that we have a lot of history from USA-S.

By trying to do our best, we attempt to eliminate pools that are without a question short. Most errors using a tape will cause the measurement to be longer than reality and therefore few pools should be falsely eliminated. There are two obvious exceptions to this: a bad tape and measurements in a high temperature. The former should be checked if one fails a pool and the latter can be corrected if necessary. As far as the errors the other way, a sagging tape was mentioned. At the 50-meter distance, the amount of sag necessary to make a significant difference is actually quite a bit (> 0.3 meters). Ignoring that the sage is not triangular (which means that the calculation overestimates the error), the error is less than 4 mm. With half that sag in a 25-meter pool, the error is under 2 mm.

Someone stated that USMS has no tolerances. The tolerance is -0.00 meter. That means that the pool must be less than 0.005 meters short. We set no maximum (after some debate) because we did not want to exclude any more pools than necessary.

Lasers have always presented a dilemma. Some bodies want to use them exclusively and I have advised them otherwise. I know that USA-S has used them for certifying a number of pools used in their championship and grand prix meets. Personally, the work required to set one up makes me want to go buy a tape.

I attended the "Our Kids Initiative" meeting last weekend in Indianapolis. In attendance were representatives from NFHS, NCAA, YMCA, NISCA, USA-Swimming and USMS. This was our first year being invited to this three-year-old gathering. The first topic on the agenda (at least the real part) was certification of pools. After the mess in Virginia Beach last year, it has become a major topic. Unfortunately, USA-Swimming doesn't have to worry too much since they don't set too many records. These other organizations only worry about the "big meets" and they do go out and spend the money to have a professional do the measurements. This includes measuring the bulkhead for every session if necessary.

So the bottom line here, IMHO, is that there are no simple answers even if you define what the true goal is. There are no acceptable answers to some of the questions.

Leo

Conniekat8
May 19th, 2004, 07:25 PM
Oh, One more thing Mattson...
It's important that we start differentiation between the actual lasr beam and the coloquialisam 'lasers' as a generalized piece of equipement that people talk about.
When they talk about 'laser' a lot of people end up refering to the little cheap hand held distance meter, which is based on laser measurements, but which has a different grade laser beam than the high precision equipement.
There is a whole array of qualities there.

What is frequently refered to as 'laser' in my business is the low end equipement. The higher end equipement still has infrared spectrum laser based technology on it, in part complemented by radio equipement as well.

Scansy
May 19th, 2004, 07:58 PM
I wish I swam fast enough for 2mm or 0.01 seconds to be meaningful!:D

Phil Arcuni
May 20th, 2004, 12:58 AM
Hey Leo, where were you and your white paper when I claimed that -.00 meters meant that a pool could be 5 mm shorter than the nominal length? You remember, that time when I was called denegrating names and told that it really meant the pool could not be 0.0000000 shorter than the length?

Just a peeve, nice post.

Conniekat8
May 20th, 2004, 02:15 AM
Well.... It's simple!
We need to get more surveyors to start swimming, then we can start twisting their arms to donate services!!!

Yeah, wouldn't it be nice ;)