Not sure if this would work, but another experiment idea is to link a bunch of (identical) rubber bands together using paper clips. Connect both ends to something, such as pegs sticking out of a wall, so the ends are level. Then place a cylindrical can on the middle of the “chain.” The can should be heavy enough to bow it down. Now measure the lengths of the rubber bands along the whole chain and see how much and where they vary.
Or you could do the same with Theraband. Make marks at even intervals while it is unstretched, then “v-stretch” it and measure the distances between all the marks.