Hand goniometer

Goniometer \Go`ni*om"e*ter\, n. [Gr. ? angle + -meter: cf. F.
   goniom[`e]tre.]
   An instrument for measuring angles, especially the angles of
   crystals, or the inclination of planes.
   [1913 Webster]

   {Contact goniometer}, or {Hand goniometer}, a goniometer
      having two movable arms (ab, cd), between which (at ab)
      the faces of the crystals are placed. These arms turn
      about a fixed point, which is the center of the graduated
      circle or semicircle upon which the angle is read off.

   {Reflecting goniometer}, an instrument for measuring the
      angles of crystals by determining through what angular
      space the crystal must be turned so that two rays
      reflected from two surfaces successively shall have the
      same direction; -- called also {Wollaston's goniometer},
      from the inventor. Goniometric