Left side numbers are inches, right side ones are cm. Center rows are magnification ratios for three different focal lengths. Just pick a pointer on the left or right side and jot the number in your notes about the print. Easy to calibrate, put a 35mm carrier in, move the head until the image is 8or 10 inches high on the baseboard, and see what points to the 8 or 10 in the column under 50.
Edit, I just write down the cm one in my notes along with the lens I am using, sometimes.