Abstract: After an operator has focused the zoom lens assembly of an optical measuring system on a workpiece, the zoom lens itself is adjusted to select a desired magnification. A reticle image in the form of a plurality of radially spaced, concentrically disposed circles is then projected, at the selected magnification, and via the zoom lens and a video camera, to a microprocessor (CPU), which electronically stores that particular image of the reticle for subsequent use, whenever it is desired to have the now-calibrated magnification reestablished. To reestablish the calibrated magnification at a later time, a new image of the reticle is projected to the CPU, and via the CPU onto a video screen. The previously recorded image of the reticle is also projected onto the video screen by the CPU, and is visually compared with the new reticle image. The zoom lens is then adjusted until the two images are coincident, at which time the previously selected magnification will have been reestablished.