Where-
Am = measured alinement deviation from uniformity (outward is positive, inward is negative).
AL = allowable alinement limit as per § 213.327(c) (always positive) for the class of track.
Sm = measured profile deviation from uniformity (down is positive, up is negative).
SL = allowable profile limit as per § 213.331(a) and § 213.331(b) (always positive) for the class of track.
49 C.F.R. §213.332