The letters on the dial are a custom option that was offered by Elgin. Usually they have some meaning to whoever commissioned the original purchase of the watch. The 'formulas' you are referring to are actually coding by watch repair guys stating they have done a service on the watch at some point. The watch case was made by the Star Watch Case Company who were based in Elgin, Illinois and existed from 1899 - 1982.
What is the serial number on the watch movement itself ? With that i can provide some further information.
What is the serial number on the watch movement itself ? With that i can provide some further information.