What is "equating for grades"

Grade \Grade\ (gr[=a]d), n. [F. grade, L. gradus step, pace, grade, from gradi to step, go. Cf. Congress, Degree, Gradus.]

1. A step or degree in any series, rank, quality, order; relative position or standing; as, grades of military rank; crimes of every grade; grades of flour.

   They also appointed and removed, at their own pleasure, teachers of every grade.
   --Buckle.

2. In a railroad or highway:

   1. The rate of ascent or descent; gradient; deviation from a level surface to an inclined plane; -- usually stated as so many feet per mile, or as one foot rise or fall in so many of horizontal distance; as, a heavy grade; a grade of twenty feet per mile, or of 1 in 264.

   2. A graded ascending, descending, or level portion of a road; a gradient.

3. (Stock Breeding) The result of crossing a native stock with some better breed. If the crossbreed have more than three fourths of the better blood, it is called high grade.

   At grade, on the same level; -- said of the crossing of a railroad with another railroad or a highway, when they are on the same level at the point of crossing.

   Down grade, a descent, as on a graded railroad.

   Up grade, an ascent, as on a graded railroad.

   Equating for grades. See under Equate.

   Grade crossing, a crossing at grade.

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.