What is an ocular micrometer?

An ocular micrometer is indeed a ruler installed in the eyepiece of a microscope. It is a precise tool used to measure the size of small objects that you would observe under the microscope, such as cells or microorganisms. The micrometer typically consists of a glass disk with a scale etched onto its surface, which is superimposed over the field of view when looking through the microscope.

This allows the user to estimate the size of specimens directly while viewing them at high magnification. The scale on the ocular micrometer can be calibrated against a stage micrometer, which is a slide with a known scale, to ensure accurate measurements. Understanding the ocular micrometer's function is crucial in microbiology when measuring and comparing the dimensions of cells or structures, aiding in morphological identification and assessment.