The Collaborative International Dictionary of English v.0.48:

Inclinnometer \In`clin*nom"e*ter\, n. [Incline + -meter.]
   (Magnetism)
   An apparatus to determine the inclination of the earth's
   magnetic force to the plane of the horizon; -- called also
   inclination compass, and dip circle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dip circle
    n 1: a measuring instrument for measuring the angle of magnetic
         dip (as from an airplane) [syn: inclinometer, dip
         circle]