Abstract: A measurement module projects into a microscope a fiduciary image having a visually extensive area. Measurements are made by translating the fiduciary relative to the object between two positions in which different fiduciary image boundaries are tangent to respective object image sides, as determined by null positions in which neither dark overlap nor bright separation zones appear between the two semi-transparent images. The width of the object can be determined from the distance of relative movement of the fiduciary between these positions. In preferred form the fiduciary image has first and second boundaries in fixed relation at a predetermined spacing and the measurement is corrected by the spacing between the two fiduciary boundaries.