Measurment of materials with the microscope involves the use of a micrometer eyepiece with micrometer disk and a stage micrometer. We have eyepiece micrometers for most of our instruments. They have graduated scales which must be calibrated against a stage micrometer for each objective or magnification that will be used.

The eyepiece micrometer has a series of arbitrary divisions and the stage micrometer is usually 1 mm divided into 100 equal parts. First focus the micrometer eyepiece till you see a sharp image of the disk. Next put the stage micrometer on the microscope stage and focus it, setting up Köhler illumination as described in steps 5 and 6.

Next align the scales in order to find out how many stage micrometer divisions equal a number of eyepiece divisions. In this example 70 divisions of the eyepiece micrometer equals 0.4 mm (400 µ) on the stage micrometer. Dividing 400 by 70 tells us that each division of the eyepiece micrometer therefore equals 5.7µ. If we measure a structure and find that it is 12 eyepiece divisions in length that equals 68.4µ (12 x 5.7).

Stereo microscopes are calibrated the same way except that a stage micrometer with a 10mm scale divided into 100 parts is used. Often a photograph of the stage micrometer is made at the same magnification as the micrograph and it can then be used as a direct "ruler" for measurements. In addition software such as ImagePro Plus can be calibrated with a stage micrometer in order for direct measurements to be made using the software's own tools.

A useful strategy for putting scale bars onto your final pictures is to photograph a stage micrometer at the same magnification as your other pictures. Open both the scale bar picture and the other pictures in Photoshop, draw the scale bar on the micrometer picture using its graduations to get the right length and then drag it from the micrometer picture to the other pictures.