Three-coordinate measuring instrument refers to an instrument that can express the measuring ability of geometric shape, length and circumferential division in a hexahedral space, also known as three-coordinate measuring machine or three-coordinate measuring bed.

A three-coordinate measuring instrument can also be defined as an instrument with a detector that can move in three directions and on three mutually perpendicular guide rails. The detector transmits signals in a contact or non-contact manner, and the three-axis displacement measurement system (such as grating ruler) calculates each point (x, y, z) of the workpiece through a data processor or computer and measures various functions. " The measuring function of three-coordinate measuring instrument should include dimensional accuracy, positioning accuracy, geometric accuracy and contour accuracy.