The TS series objective lens scale ruler of Oplin is made of German Schott B270 optical glass, which has high thermal stability. Whether in winter or summer, the length extension error of the scale is within 0.3%. The scale adopts metal coating technology, with high light shielding rate, clear lines without broken lines, and can be preserved permanently. The TS-M7 is a metric double-scale straight-line scale ruler that can be used for magnification calibration of stereo microscopes (the scale line is up to 10mm).