Aerosonic cockpit clock.  Very desirable collector's item found in virtually every type airline aircraft flown during the pre-glass era.  Convair 880, 990, 707, 727, 737, some 747's, some Convair 600's and 580's, DC-8, DC-9, MD-80, Caravelle...probably more.  RARE!
 
United Airlines parts tag.