I need help on how to level the ground for an above ground pool. i have a level that can be attached to a string but i dont know quite how to use it. the area is 18' in diameter. The instructions on the pool merely says "choose a level area." By Eyeballing the area, it seemed level but after i put the water in the pool there was a 4" difference of depth from one side to the other & you cant compensate by adding water to fill the low side because the high side will overflow! i drained the pool to start over & agained grated the surface knowing what parts were low & high when the water was in the pool. when i used a regular 1' long level & layed it on the ground, some areas look about a 1/2 bubble off on the level & some places were level. i dont know how much in inches of water a 1/2 bubble will compute to when the pool is filled again. how do i use a string level,if thats what i should be using? help!! i didnt know it would take an engineer to put up an "easy set" pool that says on the box "ready for water in 30 minutes" hah!!