Light microscopic depth measurements of thick sections.

Measurements of the thickness of a thick histological section or the depth of an object within the section, can be made most easily by reading differences in the setting of the fine focus knob of a compound light microscope. Two corrections must be made to such measurements: (1) when using a dry objective, a factor of 1.5 for the index of refraction of the specimen, and (2) a correction for the calibration of the fine focus itself. In addition, several precautions should be taken to minimize errors in the readings.