We found that the "block pattern" is not uniform around the pool, so you have to actually measure from the frame of the pool. We have a 16' ultra-frame and are off about 1.5" from one side to the other (in the beginning we thought it was 4" off due to the block pattern until we actually measured it). We also have a couple of "high posts" where the ground did not settle under the legs like it did all the way around the pool. We've been up for a month now without any issues (even with all the kids sitting on and jumping off of the frame daily).