A tape-measure-like rubber band with proportional marks to easily divide lenghts into equal sections. As a side effect, you can also scale distances up and down by basic factors. Great for working with large sheets of paper, wall mounting, floor marks, in construction projects and the like.
Fleximeter
x x - 0
) I -- 1/5
( I ---- 1/4
) I ----- 1/3
( I ------ 1/2
x I ----- 2/3
I ---- 3/4
I -- 4/5
x - 1
) I -- 1/5
( I ---- 1/4
) I ----- 1/3
( I ------ 1/2
x I ----- 2/3
I ---- 3/4
I -- 4/5
x - 1