The Collaborative International Dictionary of English v.0.48:

Tachymeter \Ta*chym"e*ter\, n. [Tachy- + -meter.]
   1. (Surveying) An instrument, esp. a transit or theodolite
      with stadia wires, for determining quickly the distances,
      bearings, and elevations of distant objects.
      [Webster 1913 Suppl.]

   2. A speed indicator; a tachometer.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

tachymeter
    n 1: a theodolite designed for rapid measurements [syn:
         tachymeter, tacheometer]