Vintage Altimeter Altitude Meter Thousand Feet CAL CAI ? Red Arrow Turning Knob

Description

Vintage Altimeter Altitude Meter Thousand Feet CAL CAI ? Red Arrow Turning Knob
Unsure how to test it .. I did NOT attempt to clean or try to restore this instrument.. I did turn black knob briefly to see if it turns ( it does) there is something small rattling inside meter