The Collaborative International Dictionary of English v.0.48:

Calipers \Cal"i*pers\, n. pl. [Corrupted from caliber.]
   An instrument, usually resembling a pair of dividers or
   compasses with curved legs, for measuring the diameter or
   thickness of bodies, as of work shaped in a lathe or planer,
   timber, masts, shot, etc.; or the bore of firearms, tubes,
   etc.; -- called also caliper compasses, or caliber
   compasses.
   [1913 Webster]

   Caliper square, a draughtsman's or mechanic's square,
      having a graduated bar and adjustable jaw or jaws.
      --Knight.

   Vernier calipers. See Vernier.
      [1913 Webster]