Gage or Gauge? Which is correct in the aviation industry? Gage or Gauge? 

Some official aviation sources seem to use the spelling "gage" whether referencing cockpit instruments or aircraft maintenance tooling.

However, more broad English sources note that "gage" is either interchangeable with "guage," or flat out incorrect.

Is either spelling technically correct, or only one? 

Do the different spellings hold different meanings or connotations in aviation? 

Are there official examples that could make the argument "gage" could be correct in specific circumstances (patents, manuals, industry standards, trademarks)? 

Is there a history in early aviation using "gage" that has been carried over unofficially to today (like how older aircraft operating today may have mph on their airspeed indicator)?
Gauge is correct. As in Oil temperature gauge, Fuel Pressure gauge, Fuel Level gauge, Cylinder Head Temperature gauge, Exhaust Gas Temperature gauge, etc.

Anyone use gage is misspelling the word.  Same with Hangar. (Not hanger)