the easiest way I know of to check for level is to use a STRAIGHT 2X4 and a level. For a 16' pool, get a 10' 2"X4" and drill a 1/2" hole about 1' from one end. This will give a bout a 1' perimeter around the pool that has been leveled which will ease setting the blocks for the legs.
Drive a stake in the center of the pool area
http://www.lowes.com/pd_17199-157-05...r|1&facetInfo=
then fit the stake through the hole in the board. You can now rotate the board around the circle with a level on top of the board. This will show low and high spots and over all level (or lack thereof) of the area. A 9" torpedo level would work, but a 2" level would be better.
http://www.homedepot.com/p/Johnson-2...1?N=5yc1vZc1zq

Good Luck!

Pappy