Keuffel & Esser Stadimeter/ Range Finder Marine Navy Device

Description

This old piece is in used condition as shown.
There are some stains and signs of wear and tear.
There is a light bulb socket that came apart while handling,
please look at the last picture.
The serial number stamped looks like 33813 A.
This part came from an USMC retired paratrooper.
I don't know how it works, so please ask any question and if i did not
answer, please ask again, because the system is bad and when i read
the question i do need answer immediately or don't let me do it.
Thanks for looking.