University of Nebraska-Medical Center
Clinical Laboratory Science Program
CLS 418 & 419
Page 1 of 1
For student use only
Procedure for Calibration of Microscopes
Using an Ocular Micrometer
Place the stage micrometer on the microscope stage and focus on the micrometer scale, until you
can distinguish between the large (0.1 mm) and the small (0.01 mm) divisions of the scale. Adjust the
stage micrometer so that the "0" line on the ocular micrometer is superimposed with the "0" line on
the stage micrometer. Without changing the stage adjustment, find a point as distant as possible
from the two superimposed "0" lines where two other lines are also exactly superimposed. Determine
the number of ocular micrometer spaces, as well as the number of millimeters on the stage
micrometer, between the two points of superimposition.
For example: Suppose 48 ocular micrometer spaces (units) equal 0.6 mm. Calculate the number of
mm/ocular micrometer space.
0.6 mm x 48 ocular micrometer spaces = 0.0125 mm/ocular micrometer space
Since most measurements of microorganisms are given in µm rather than mm, the value calculated
above must be converted to µm by multiplying it by 1000 µm/mm.
For example: 0.125 mm ocular space x 1000 µm/mm = 12.5 µm/ocular micrometer space
Thus in this case, 1 ocular micrometer space (unit) is the equivalent of 12.5 µm.
Follow the above steps for each objective. Calibration readings should be posted on each
microscope and the microscope should be recalibrated after every cleaning or changing of objectives
or oculars.