Source : Webster's Revised Unabridged Dictionary (1913)

Equate \E*quate"\, v. t. [imp. & p. p. {Equated}; p. pr. & vb.
   n. {Equating}.] [L. aequatus, p. p. of aequare to make level
   or equal, fr. aequus level, equal. See {Equal}.]
   To make equal; to reduce to an average; to make such an
   allowance or correction in as will reduce to a common
   standard of comparison; to reduce to mean time or motion; as,
   to equate payments; to equate lines of railroad for grades or
   curves; equated distances.

         Palgrave gives both scrolle and scrowe and equates both
         to F[rench] rolle.                       --Skeat
                                                  (Etymol. Dict.
                                                  ).

   {Equating for grades} (Railroad Engin.), adding to the
      measured distance one mile for each twenty feet of ascent.
      

   {Equating for curves}, adding half a mile for each 360
      degrees of curvature.