Objective Olympus MPLN100XBD M BF, DF, Plan, Achro, Auf-Durchlicht, Oil, 100x/1.25 wd 0.21mm

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.