The Collaborative International Dictionary of English v.0.48:

Waywiser \Way"wis`er\, n. [Cf. G. wegweiser a waymark, a guide;
   weg way + weisen to show, direct.]
   An instrument for measuring the distance which one has
   traveled on the road; an odometer, pedometer, or
   perambulator.
   [1913 Webster]

         The waywiser to a coach, exactly measuring the miles,
         and showing them by an index.            --Evelyn.
   [1913 Webster]