A scanning spot (54) moves over a pair of masks (50, 58) provided with respective arrays of transverse slits (52) of varying widths along the path of the spot or of transverse windows (60) at varying positions along a line (62) at an angle (.alpha.) to the path. Pulses of light passing through the slits...http://www.google.com.au/patents/US5499094?utm_source=gb-gplus-sharePatent US5499094 - Apparatus and method for measuring the length and width of a spot of light utilizing two different masks
