# Ocular and Stage Micrometers

Calibrating an ocular micrometer is only reliable for one objective on one scope.  Changing the objective lens or using a different scope than your assigned scope may yield varying results.  Always calibrate your micrometers when using new objectives or different microscopes.
Each division of the stage micrometer = .01mm.
Formula:
[(# divisions counted on stage micrometer)(one division of the stage micrometer in mm)/(# divisions counted on ocular micrometer)][1000]

Example 1
.01mm stage micrometer
stage micrometer = 12 divisions to 22 divisions on the ocular micrometer
Step 1:  [(12)(.01)/(22)][1000]
Step 2:  (.12/22)(1000)
Step 3:  (.0055)(1000)
Equals:  5.5µm per ocular division

Example 2
.01mm stage micrometer
stage micrometer = 1 divisions to 7 divisions on the ocular micrometer
Step 1:  [(1)(.01)/(7)][1000]
Step 2:  (.01/7)(1000)
Step 3:  (.0014)(1000)
Equals:  1.4µm per ocular division

Problem 1
You have calibrated your ocular micrometer.  Each division of the ocular micrometer equals 1.4µm.  You count 5 divisions of the ocular micrometer as the length of an individual specimen.  How long is this specimen?

Formula:  Total specimen length (x) = (length of one division of the ocular micrometer)(number divisions counted as length of an individual specimen).
Step 1:  x = (1.4µm)(5 divisions)
Step 2:  x = 7µm

Note:  In unknowns, if your organism is 7µm in length, does that length fall within the known lengths for the species you think you have?