# Math question

Here's another: Measure the pH of the pool water. Add a known amount of acid, and measure the pH again. Compute the volume of water from the difference in pH readings.
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snipped-for-privacy@milmac.com (Doug Miller) writes:

Well the pool presumably have additives which may act as buffers so not so easy unless you know the exact chemical composition of the pool "water".
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Errm...wouldn't you have to allow for the weight of ink in various areas?

Harry K
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Nope, that would calculate volume, not area. Hving been wrong 2 out of 2 I quit :)
Harry K
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Same idea, but way less messy:
1 - Mark the water level of the pool as it is right now. 2 - Drain the pool 1/2", 3/4", 1", whatever. 3 - Refill the pool to the original line, keeping track of how many gallons it takes.
"Since you know the thickness and the volume, determining the area is trivial."
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Why do you have to drain it? Couldn't you just add 1/2" of water? It also seems odd to start playing with volumes when you want area. It could be done, but the added dimension would require you to be very precise - very precise - with the measurement of the change in water depth or the number would be as bad, or worse, as a guess.
R
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First, let's realize that we're all just tossing out possible solutions as a brain exercise.
No more than would I expect the OP to pour 55 galons of 0W20 into his pool, would I expect him to drain/refill it to determine the area.
However, to answer your specific question - "Why do you have to drain it?":
Have you seen the OP's pool? It's filled right to the top of the skimmer, so adding a 1/2" of water would put the skimmer out of commision until the new water evaporated. By that time, all the debris that the skimmer would usually handle -- leaves, suntan oil, hair -- would become a toxic waste composition that would eat away at the liner, causing deterioration of the concrete walls, resulting in a massive leak and a sinkhole that would swallow the OP's house.
With that possiblity on the table, I'd suggest draining off the 1/2".
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Good idea! Then to get rid of the oil you just toss in a hose and let it overfill till the oil is gone. Oh hell, even a forest flattened from fire comes back. The pond surroundings should come back...eventually.
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Looks like from all the replies you're gettin' too much info here Steve. Here's a simple solution.
Look at perimeter from a distance. Hold arm straight out with thumb up. Line up thumb with eye and shape. Pull number out of your ass...like maybe 42. Yer dun.
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Isn't 17 the correct answer to everything? (Hitchiker's Guide to the Galaxy).
Harry K
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No, that's where "42" came from.
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Doug Miller wrote:

But there were three books in the series. Three times 17 is 42 (or close enough).
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Well I pulled it outta my ass. What do you expect? Just because I can talk out of my ass doesn't mean I have an intelligent asshole.
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SteveB wrote:

The skimmer on my neighbors' pool has a throat 145mm high. If I put the end of a white plastic ruler against the bottom of the throat, the ruler looks bluish below the waterline and pinkish above. This makes it easy to read the depth of water in in the throat with a precision greater than 1 mm.
Now see what units your water meter measures. Wait until the water is near the bottom of the skimmer throat. Write your depth in mm. Write your meter reading.
Fill. Write your new depth and meter reading. See how much water was used and convert to liters. Divide that by mm to get square meters within 1%.
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E Z Peaces wrote:

Ideally, choose a windless, overcast day when the water temperature is near the dew point.
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Just out of curiosity, have any of you ever seen a pool where there are absolutely no ripples and the water level isn't heaving even a little from some sort of hydraulic pendulum effect?
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mike wrote:

When I checked my neighbors' pool today I got a constant reading on my ruler, precise to .5mm or so. There was some rippling where filtered water was being returned to the pool, and the wind may have been 1 mph.
On a day when the water temperature was 85F and the dew point was 60F and the wind 10mph, if it took hours to raise the water level, I imagine you could lose enough from evaporation to make area calculations meaningless.
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I'll phrase my words carefully - what a load! 1/2 millimeter. Please. The water in a bathtub couldn't be measured to that degree of accuracy. The surface tension of the water alone would throw the reading off by at least that much.
Interesting that you would use the word precise instead of the word accurate. Precise has connotations of repeatability, and I have no doubt that your eyes, system and predilections would cause you to read accuracy into something that isn't.

Measuring a volume makes an area calculation meaningless in something where you can't accurately measure the change in depth. If you want to measure an area, measure an area. Don't add another variable and expect it to be more precise or accurate.
R
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RicodJour wrote:

Why do you keep talking about accuracy? If I wanted to know the water level, I would have to take the meniscus into account. Who cares about the water level? All I need to know is the change.
I've been reading rules to the nearest 1/2 mm for decades, fabricating pieces for household repairs. My readings have always been repeatable.
I'm used to reading the level at the skimmer so I can predict when I'll need to shut the water off. Yesterday I checked to see how precisely I could read. With the material of my ruler, I didn't know if the meniscus would be up, down, or flat. I didn't if it would be hard to see the waterline or if the level would move.
As it was, the change in color made a distinct line across the white ruler. It could be read precisely and repeatably.
In ancient Greece, a philosopher like you would have had a mechanic like me executed for testing a theory by experiment.
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Why talk about accuracy in a calculation...? Forget it. I have no reply for that.

Household repairs and you're working to two hundredths of an inch? What's your house milled from - a block of aluminum? Again, please. If you're working on a milling machine you measure to the thousandth, almost everything in home repair can be measured to the 1/16, or 1/32 if you're anal. After that it's just wasted.

No. That's not the reason I'd have you executed. :)
R
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