1.1.4—Microscope measurement tools

An eyepiece graticule is an arbitrary scale in the microscope view. A stage micrometer calibrates how much real distance one graticule division represents at the current magnification.

1. Superimpose the graticule and stage-micrometer scales.
2. Choose a matching interval and record its real stage-micrometer distance.
3. Divide that real distance by the number of graticule divisions to obtain the factor.
4. Count specimen divisions and multiply by the factor.
5. Recalibrate whenever the objective or magnification changes.

If 20 graticule divisions coincide with 0.20 mm on the stage micrometer, one division is 0.010 mm = 10 µm. A chloroplast spanning 4 divisions is therefore 40 µm at that setting.

The eyepiece scale is not automatically in micrometres and is not calibrated by magnification alone. The same number of divisions can represent a different length after the objective is changed.