Re: Numerical Mysteries

Doug,

I understand your point about tolerance. Everything I said about gage above refers to nominal gage, exclusive of any effect of tolerance. So when I suggested that a three-foot-gage railroad might purchase a locomotive built to 35.5-inch-gage (for better running on curves), I mean nominal gage in both the locomotive and the track. So in terms of the nominal gage, they differ by ½ inch. I realize that they both may fall within the tolerance of each other. However, if the two gages are assumed to be nominal, their respective tolerance ranges will not fully coincide.

In the same way, I would not refer to the Pennsylvania RR 57-inch-gage as standard gage just because it falls within the tolerance of 56.5-inch-gage (if it does fall within that tolerance).