double-pan mechanical balance is used to compare different masses. Usually an object with unknown mass is placed in onepan and objects of known mass are placed in the other pan. When the bar that connects the two pans is horizontal, then the masses in bothpans are equal. The “known masses” are typically metal cylinders of standard mass such as 1 gram, 10 grams, and 100 grams. (credit:Serge Melki)