Start by driving two sturdy stakes opposite each other on either side of the pool location. Have the stakes at least 1 foot above ground. Tie a string between the two stakes and place the level in the middle of the length of string (this is important so the string doesn't have to be pulled extremely tight. Move one end of the string up or down on the stake until the level indicates level. You can now measure with a tape measure from the string to the ground. if the ground is level, the measurement will be the same along the entire length of string. You can repeat this process at different points around the diameter. Good Luck! Dodgeman