GB266226A - Improvements in and relating to optical scale reading devices - Google Patents

Abstract

266,226. Wilson, J. S., Linn, J. D., and Taylor, E. W. Aug. 31, 1926. Indicating, optical devices for.-A device for determining the mean reading of two scales or scale images disposed adjacent to one another comprises a translucent diagonal scale displaceably mounted relatively to the main scales and provided with a reading index line or lines extending from the zero indication of the scale and parallel to the main indications. The diagonal scale is graduated so that a minute division on the scale subtends two minutes on the main scales; it is marked or engraved on a sheet of glass 1, Fig. 1, mounted in an eye-piece frame 2 and adjustable by means of a knob 3. As shown in Fig. 2, the diagonal scale is constituted by lines 8 - - 10 with reading index lines 11 at one end which can be brought into coincidence with the nearest coarse graduation oi the projected main scales 4 or 5. The true mean reading is obtained on the diagonal scale by setting the actual or virtual index 7 to the left of the lines 11 and by reading to the lower scale division immediately to the left of the index 7. The diagonal scale may be twice the length of any two coarse graduations to avoid errors in reading and it may be displaceably mounted in two directions at right angles so as to bring it to the position shown in Fig. 8 thereby facilitating the reading of the minute divisions. The diagonal scale may take the form of a single inclined line 11, Fig. 9, subdivided by lines 12. In use with circular main scales the lines 10 of the diagonal scale will not be parallel but will radiate in accordance with the curvature of the main scales.