Inground fiberglass pool - how level does it need to be?

I'm having a local contractor put in a fiberglass mfg inground pool. They started with a bed of sand and seemed to be checking for level. after a bit of sand they made some adjustments with some jacks on the corners.
Now that it's about 2/3 full of water (and sand around the edge), it seems like the pool is not 100% level. I used a small torpedo level and I could see that it was not completely level (still inside the big square, but not completely center), and realize that at 15 ft, a larger level might show even greater amount off.
This is a stupid question but,
#1 - how can I best verify how far off level it is without investing lots of money?
#2 - how important is it that this type of pool be close to 100% level before they pour the concrete up to the edge and finish up?
Thanks!
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Put the torpedo level back where you found it. Use a water level, piece of 3/8 tubing filled with water. Check level with that. Torpedo's are used for small or short distances. Ever wonder why most carpenters use 4 foot and 8 foot levels for walls?
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Put away ALL the levels and use a tape measure! He said the pool is about 2/3 full of water, so measure from the water's surface to the top edge of the pool! Greg
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To be perfectly precise you could get a level float to check the water surface. <grin>
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