Angle indicator with two pairs of scale discs - which are at right angles to each other, and have mirror reflecting image of one pair on plane of other

摘要

The indicator indicates angles in two directions perpendicular to each other and has two angle indicating devices, each with two scale discs with opaque lines separated by transparent spaces. The scale discs are parallel to each other, so that Moire patterns are produced when light passes through the discs. One disc is stationary and the other can rotate freely. Two pairs of scale discs (1, 2) are placed in planes perpendicular to one another. A mirror (26) projects the image of the second scale disc pair (2) on the plane (27) of the first pair (1) near to it, so that the two Moire patterns appear to lie next to each other.