A proof mass or test mass is a known quantity of mass used in a measuring instrument as a reference for the measurement of an unknown quantity.
A mass used to calibrate a weighing scale is sometimes called a calibration mass or calibration weight.
A proof mass that deforms a spring in an accelerometer is sometimes called the seismic mass. In a convective accelerometer, a fluid proof mass may be employed.
See also
Calibration, checking or adjustment by comparison with a standard
Control variable, the experimental element that is constant and unchanged throughout the course of a scientific investigation Test particle, an idealized model of an object in which all physical properties are assumed to be negligible, except for the property being studied