Reticle A is designed for general laboratory use (5 mm long, with 0.1mm divisions) and reticle B (4/16" long, 1/64" divisions) is most frequently used in textiles or electronics, and where measurement in mils is required. Reticle C (5000 µm long, with 50 µm divisions) is calibrated in microns and helpful for pesticide droplet size measurements or anywhere measurements in microns are required.