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
Caliper square, a draughtsman's or mechanic's square,
having a graduated bar and adjustable jaw or jaws.
Vernier calipers. See Vernier.