GB574295A - Improvements in scale-reading means for angle measuring instruments or devices - Google Patents

Abstract

574,295. Theodolites &c. WATTS & SON, Ltd., E. R., and GODFREY, C. J. Jan. 27, 1944, No. 1555. [Class 97 (ii)] In a theodolite or other angle-measuring instrument wherein two opposite parts of a divided circle are read simultaneously in a reading microscope the two images appearing in the field of view in juxtaposition running parallel to each other in opposite directions, the scale image from one side appears as a row of single divisions while the scale image from the other side appears as a row of double lines, one scale image only being movable for the purpose of bringing the double lines of one image into a position in which they straddle a single line of the other image in order thereby to facilitate the obtaining of exact coincidence. As shown in Fig. 1, the two images from the opposite sides of a divided glass circle h may be formed by light from a mirror g passing through a reflecting prism i, a series of microscope objectives k, a refractor l and reflecting prism m. The images are viewed through the eye piece lenses p and objectives o of a micrometer microscope, the resulting picture being of the nature seen in Fig. 6 where double lines of one image , straddle single lines of the other image e, the images being viewed simultaneously with the micrometer scale o<1>. The refractor l is connected by cam and lever mechanism to the micrometer scale o<1> and is moved therewith to effect the movement of one of the scale images.