IMA/USP Microscope Counting Reticle

The IMA/USP counting reticle is used for manual particle counting, most often in the pharmaceutical industry. Government guidelines (USP 788 Government Standards) require a manual microscope particle counting system must include a circular diameter reticle (installed in the microscope eyepiece) that is designed specifically for this purpose and calibrated using a certified stage micrometer.

The IMA/USP particle counting reticle is divided into four quadrants by crosshairs - each showing transparent and black reference circles 10um and 25um in diameter at 100x magnification. 

When manually counting particles, the user will place the filter under the microscope with the counting reticle in the eyepiece. By carefully comparing any particles seen under the microscope to the reference circles, the user can record the number of particles of particular sizes.

You can learn more about IMA/USP Counting Chamber microscope reticles here.