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How to Calculate Calibration Using a Stage Micrometer

Many microscopes come equipped with a scale built into one of the eye pieces that allows the user to measure microorganisms. This ocular scale is called a reticule and can be turned in any direction by simply rotating the microscope's eye piece. The reticule must be calibrated before use to accurately measure the desired subject. This is accomplished using a stage micrometer, which is a slide that has a scale etched onto the surface. By calibrating the reticule using one of the microscope's objectives, it is then possible to calculate the calibration for the other objectives.

Instructions

- 1
  Slide the eye pieces of the microscope closer together or farther apart so when you look into the eye pieces you only see one field.
- 2
  Locate the reticule in one of the eye pieces and turn the knob that wraps around the base of the eye piece to bring the scale into sharp focus. Rotate the microscope's objectives so that you are looking through the 10 power objective.
- 3
  Set the stage micrometer directly on the microscope's stage and clamp the stage clips around the stage micrometer to hold it in place. Turn the coarse and fine focus knobs located on the side of the microscope to bring the stage micrometer's scale into focus.
- 4
  Turn the stage transport knobs located on the base of the microscope's stage. Slide the stage to line up the divisions on the stage micrometer with the divisions on the reticule. Count how many reticule scale divisions are between two micrometer divisions.
- 5
  Look on the stage micrometer to identify how many millimeters each division on the stage micrometer equals. Multiply this number by 100 to convert the measurement into micrometers.
- 6
  Divide the measurement arrived at in Step 5 by the number of divisions you counted on the reticule. This tells you how many micrometers each line on the reticule equals using a 10 power objective, which has a total magnification of 100
- 7
  Multiple the number on the other objectives by 10 to determine the total magnification of each objective. The 4-power objective has a total magnification of 40
- 8
  Divide 100 by the total magnification of each objective and multiply this number by the number of micrometers each line on the reticule equals. One hundred divided by 40 equals 2.5 and you'll need to multiply this number by 10 if each reticule division measures 10 micrometers. On the 4-power objective, each line on the reticule equals 25 micrometers.

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