3,243. Terumas Maaser
Terumos 3:9
Let’s say that someone declares, “The terumah for this pile of grain A is here (indicating a spot) and the terumah for pile of grain B is like A.” In such a case, the spot where terumah for the pile A ends, the terumah for pile B ends at the analogous spot.
Terumos 3:10
Terumas maaser is not taken by estimate. Rather, one must be exacting, even nowadays, because the amount to take is explicit in the Torah.