what would the reason be for a graduated cylinder to have 2 sets of scales on it, one rising by 10s and one lowering by 10s? for ex, on one side from the bottom- 10, 20, 30, etc. then on the other side from the bottom- 90, 80, 70, etc.

It is silly of course, but some like to know how much they have put in whilst others like to know how much they have poured out.