Balance for weighing very small objects WordNet 3.0 & Open English WordNet

A microbalance is an instrument capable of making precise measurements of weight of objects of relatively small mass: of the order of a million parts of a gram. In comparison, a standard analytical balance is 100 times less sensitive; i.e. it is limited in precision to 0.1 milligrams. Wikipedia

Any balance capable of weighing objects having a mass less than a milligram. Wiktionary

Balance capable of weighing objects having a mass less than a milligram. Wiktionary (translation)