I would like any suggestions on how to do this with a tape. (This is pretty non controversial, right?) I have spent a career trying to figure out how to measure things, and I am curious. From the comments in this group, the problems I mention below must have been solved.
First you stretch the tape along the side of the pool. That would work well, but how are you sure you are aligned with the walls, or that the walls are square? Also, you need to measure in several lanes, rather than the side.
So you get in the pool and hold the tape against the walls, 1 foot below water level. The problem is that the tape sags, and any measurement will overestimate the length of the pool by a significant amount. You could pull the tape tighter, but I suspect before the tape gets tight enough, your tape will stretch or break. (I used to assign that as an intro physics problem). I suppose you could build a support structure across the pool, but that would be a pain in the neck, and you would have to move it from lane to lane.
Getting the water out of the pool would make that support structure easier, but the water weighs a lot. It almost certainly causes the walls to bend outward, especially in the deeper pools. (How do the people who design above ground, temporary competition pools do it?) I don't know how much the walls will move, but how do you account for that? (and by the way, how do the masons make sure their plaster/tiling is correct in an empty pool?)
Here is an idea - you lower the water level by a foot or so, and build a *floating* support structure for the tape. I think that would solve most of the problems. Has anyone done that?
Parents
Former Member
Originally posted by osterber
Well, I've measured a couple of pools with the Disto Pro, and signed my name to several pool length certification forms as fully believing that my measurements were accurate to the tolerances specified by USMS.
No, I'm not a certified surveyor, and never claimed to be. I feel a whole lot more confident with our laser measurements than I was with any metal tape measurements we did before.
-Rick
Confidence in measurements, as you describe it to me sounds very subjective.
Professionaly speaking, when it comes to having confidence in measurements, there is no room for subjectivity. There is a set of procedures that needs be followed to assure a certail level of precision, and the set of procedures depends on a desired precision.
At that point, something measured, you don't get just 'subjectiove confidence' you get mathemathically substantiated 'level of certainty' that can be certified to 95%, 90%, 80% (etc.)
As a surveyor, I can tell you that there are many situation in which I can get much higher level confidence measurements then with a laser. There are sutuations where it just the opposite, and the laser may be the equipement of choice.
As far as you signing of on the measurements would be like me signing off on someone's coaches certification...
You don't have the authotiry on the former, I don't have theauthority for the latter.
That's just another absurdity in the pool length certification rules, as written. They require extremely (and in my opinion very un-necessary) level of precision (which does not assure the accuracy), but on the other hanmd, they accept just about anyone signing off on the measurements.
Technically, it's ludocuous, and if anyone ever seriously challenges their time or a record based on the pool length, challenging the way USMS does pool certifications in court, or arbitration, by even a half baked professional in that field will be a child's play.
So, even if it is probably very far fetched, I do see a potential legal issue here.
Couple of questions...
You say that you are confident that your measurements are within the tolerances of what USMS requires? How is that?
What;s your level of certainty, and what is your error factor? Can you plot the error elopses? How many repetitions did you use in your mesurement? How did you interpret the repetions, did you average them out, or did you use least squares adjustment?
Do you know that as written, USMS rules don't allow for any tolerances in the measurements, event the tolerance that the manufacturer claims on the equipment that you use.
Did you know that the manufacturer's tolerance indicates the best case scenario, ideal conditions in a testing lab, and that in real live measurements you can expect that error to at least double.
Did you know that by signing a 'certification' you can be held legaly liable for the accuracy of the measurement that you're unable to substantiate. Did yuou know that by signing for a measurement you may end up being found as "practicing land surveying without a license" and that you could find yourself fined (In California for example) $500 dollars, or may be imprisoned for up to 30 days... and (not that it would matter to a lay person) get suspended from ever becoming a professional land surveyor.
Anyway, I'm playing a devils advocate here, and portraying the worst case scenario... my point being, the way the measurements are done within USMS right now, if any of it ever ends up in court, that's what you can expect.
Originally posted by osterber
Well, I've measured a couple of pools with the Disto Pro, and signed my name to several pool length certification forms as fully believing that my measurements were accurate to the tolerances specified by USMS.
No, I'm not a certified surveyor, and never claimed to be. I feel a whole lot more confident with our laser measurements than I was with any metal tape measurements we did before.
-Rick
Confidence in measurements, as you describe it to me sounds very subjective.
Professionaly speaking, when it comes to having confidence in measurements, there is no room for subjectivity. There is a set of procedures that needs be followed to assure a certail level of precision, and the set of procedures depends on a desired precision.
At that point, something measured, you don't get just 'subjectiove confidence' you get mathemathically substantiated 'level of certainty' that can be certified to 95%, 90%, 80% (etc.)
As a surveyor, I can tell you that there are many situation in which I can get much higher level confidence measurements then with a laser. There are sutuations where it just the opposite, and the laser may be the equipement of choice.
As far as you signing of on the measurements would be like me signing off on someone's coaches certification...
You don't have the authotiry on the former, I don't have theauthority for the latter.
That's just another absurdity in the pool length certification rules, as written. They require extremely (and in my opinion very un-necessary) level of precision (which does not assure the accuracy), but on the other hanmd, they accept just about anyone signing off on the measurements.
Technically, it's ludocuous, and if anyone ever seriously challenges their time or a record based on the pool length, challenging the way USMS does pool certifications in court, or arbitration, by even a half baked professional in that field will be a child's play.
So, even if it is probably very far fetched, I do see a potential legal issue here.
Couple of questions...
You say that you are confident that your measurements are within the tolerances of what USMS requires? How is that?
What;s your level of certainty, and what is your error factor? Can you plot the error elopses? How many repetitions did you use in your mesurement? How did you interpret the repetions, did you average them out, or did you use least squares adjustment?
Do you know that as written, USMS rules don't allow for any tolerances in the measurements, event the tolerance that the manufacturer claims on the equipment that you use.
Did you know that the manufacturer's tolerance indicates the best case scenario, ideal conditions in a testing lab, and that in real live measurements you can expect that error to at least double.
Did you know that by signing a 'certification' you can be held legaly liable for the accuracy of the measurement that you're unable to substantiate. Did yuou know that by signing for a measurement you may end up being found as "practicing land surveying without a license" and that you could find yourself fined (In California for example) $500 dollars, or may be imprisoned for up to 30 days... and (not that it would matter to a lay person) get suspended from ever becoming a professional land surveyor.
Anyway, I'm playing a devils advocate here, and portraying the worst case scenario... my point being, the way the measurements are done within USMS right now, if any of it ever ends up in court, that's what you can expect.
