nOpisometerAn instrument with a revolving wheel for measuring a curved line, as on a map.
Century Dictionary and Cyclopedia
nopisometerAn instrument for measuring curved lines upon a map. The instrument consists of a wheel turning as a nut upon a screw. The wheel, being brought hard up to a stop, or to a mark indicated by a pointer, is rolled over the line on the map so as to unscrew it, and is then rolled back over the scale to its former position.
Chambers's Twentieth Century Dictionary
nOpisometerop-i-som′e-tėr an instrument for measuring curved lines on a map.