Lensatic Army Compass - What's Inside? (4K)

[tsbrownie]

Thought you might like to see what's inside an lensatic Army type compass. I've never opened one before and it's got a few surprises.
A lensatic compass is one with a lens (for alignment with landmarks) and a dial instead of a needle.

From Wikipedia:
The military forces of a few nations, notably the United States Army, continue to issue field compasses with magnetized compass dials or cards instead of needles. A magnetic card compass is usually equipped with an optical, lensatic, or prismatic sight, which allows the user to read the bearing or azimuth off the compass card while simultaneously aligning the compass with the objective. Magnetic card compass designs normally require a separate protractor tool in order to take bearings directly from a map.[21][22]

The U.S. M-1950 military lensatic compass does not use a liquid-filled capsule as a damping mechanism, but rather electromagnetic induction to control oscillation of its magnetized card. A "deep-well" design is used to allow the compass to be used globally with a card tilt of up to 8 degrees without impairing accuracy.[23] As induction forces provide less damping than fluid-filled designs, a needle lock is fitted to the compass to reduce wear, operated by the folding action of the rear sight/lens holder. The use of air-filled induction compasses has declined over the years, as they may become inoperative or inaccurate in freezing temperatures or extremely humid environments due to condensation or water ingress.[24]

[Toolmaker51]

re: The seal, unsure replacements are available. Being US though, I wouldn't be surprised. The apparent same pattern is still GI Issue.
Knock-offs and counterfeits abound online, with very creative terms to imply USGI Std issue, right down to case markings. caveat emptor. There are still proper lensatic compasses made, many noted as 'Engineer' 'Survey' 'Orienteering'. The best alternative might be the Boy Scout Silva, needle-type but mounted to a card, instead of common bezel. Anything that offers a straight edge, perpendicular and rotating bezel is a good start, sighting a good bonus.
Current manufacturer is Cammenga https://cammenga.com/

Anything less might as well be a zipper pull.