I am trying to zero my M73B1 rifle using the instructions on pages 20 & 21 of TM 9-270 dated 28 September 1943. According to the manual part of the procedure for both windage and elevation adjustments is to turn both the windage and elevation screws clockwise as far as they will go. Next turn the screw counterclockwise until the “index” points to “0” on the windage/elevation screw. I am trying to determine exactly where this index mark is. Can anybody help me with this? Thank you for your help.

Larry