A micrometer glass equipped with a 1 mm graduation divided into 100 parts. The smallest plot is 1/100 mm (10 ?m). The micrometer glass is used in the process of calibrating the graduation of the measuring eyepiece. Calibration is performed for each lens. As a result, we obtain the micrometer scale parameter for a given microscope and lens. For direct measurements , a graduated eyepiece is used (after calibration with a calibration glass).