Nanomechanics weighs in

A better way to measure the mass of a microscopic sample is to quantify the sample's inertia as it is forced into motion. This is the principle behind mass spectroscopy, in which the trajectory of an ionized particle in a strong electromagnetic field provides a precise measure of the particle's inertia, and therefore a measure of its mass. Thus, nano-scale devices can measure masses with a precision of one attogram, which is three orders of magnitude better than the previous record.