heres an idea: let's take 53 -100ft garden hoses and hook em together. find 2 miles of relatively flat ground(the flatter the easier) from a center post, run the garden hose 1 mile in 1 direction. drive another post. attach sections of clear tubing to both ends of the hose. fill the hose with water until water line is visible in both clear tubing sections and hold them still against the posts until water settles to a stop. mark the water level mark on both posts. then take the hose and drag it in the opposite direction of the center post to a third post, 1 mile from the center, 2miles from the far post, but in line with the other two. repeat first step of filling with water and making marks. (after 2nd marks are made adjust both 2nd marks equally to match elevation of first marks.)(eg. if on middle post 2nd mark is 10" lower than first mark, raise both 2nd marks 10" to match first marks elevation) now we have 3 marks, all level to the middle post mark... shoot a laser from 1 end mark to the far end mark and then see where it intersects on the middle post relative to the mark thats been made. ( if it drops low of the mark... its round! if it is right on the mark...its flat! and if its high of the mark... its concave!) that's it! it's that simple! ( a high powered spotting scope with horizontal line could be used instead of laser also. or even a really fancy transit with 2mile range) and if you're wondering what good filling a miles worth of garden hose would do... its called a water level (water will always sit level to itself. yes even inside of a hose* so long as no section of the hose is higher than the ends) its how they leveled mobile homes for years and still do. SO... there ya have it! you know youre right! you know they're wrong! stop arguing nonsense and someone put their money where their mouth is please!