The number is printed in white on the front of the lens
overall: 1 1/4 in x 3/4 in x 3/4 in
The record contains an additional lens for the Omag, an optical device somewhat like a microscope. It was used to inspect the screen on a cathode ray tube. With it one could visually check the quality of the CRT spot. The idea was to adjust the system so that photographs of the image displayed on the screen were the best obtainable.