One who, or that which, compensates; -- a name applied to various mechanical devices.

a device in the beam path which can insert an adjustable phase shift (a delay, in effect)

a device that acts as a channel inverse, and thereby can be used to reduce signal distortions

A device that eliminates the effect of an unmeasured variable or condition on the measurement of interest.

An irregularly shaped beam modifying device utilized to reconfigure the beam intensity to match irregular tissue contours.