Should be used before Fine Specimen Focus Knob to "rough in" the Focus.
Care Should be Exercised NOT to translate Specimen into Objective Lens!
Look at Objective Lens and Specimen Slide position from the side when performing Initial Adjustments of this Knob to AVOID THIS PROBLEM!
Rotate this Knob to Translate the Specimen Stage in the Z direction, bringing the Specimen into the Focal Plane of the Condenser and Objective Lenses.