Special Features:

A clear plastic sheet with precisely spaced circles inscribed on it; it is placed over crt screen and used to adjust linearity with the pattern dots on the crt screen; required for test and alignment of the monitor; used to verify horizontal and vertical linearity alignment of the crt screen

Properties:

An item, usually made of glass, having fine wires or hairs, or etched or printed fine lines on a surface, and placed in the focal plane of an optical instrument to establish a reference point to the axis for the purpose of aiming, measuring, ranging, and the like. Excludes lens, optical instrument.