It may be necessary to get a precise measure of magnification for various purposes eg publication of photographs. A micrometer eyepiece should be calibrated using a slide with a micrometer scale. The eyepiece then can be used to measure the dimensions in micrometers of viewed specimens . When the photo-micrograph is printed out the measured object(s) can then be measured in millimeters. From this the magnification of the print can be calculated. Adjustment for any magnification produced by enlargement of the print gives the magnification of the microscope.