Source : Webster's Revised Unabridged Dictionary (1913)

Sensitometer \Sen`si*tom"e*ter\, n. [See {Sensitive}; {-meter}.]
   (Photog.)
   An instrument or apparatus for comparing and grading the
   sensitiveness of plates, films, etc., as a screen divided
   into squares of different shades or colors, from which a
   picture is made on the plate to be tested.

Source : WordNet®

sensitometer
     n : a measuring instrument for measuring the light sensitivity
         of film over a range of exposures