Head, trinonocular, Siedentopf, 30°, 100:0/0:100/20:80, (BA410E microscope)

This refers to the magnification factor of a single microscope lens. A lens with the number 40 is referred to as a scale of 1:40 or simply a factor of 40 times. If you multiply the lens factor by the eyepiece factor, you get the magnification.