A minor rant, but meant in good nature: I've hear a rumor (I'm trying to find it again, and am beginning to think it's just apocrypha) that the NMRA is pushing the spelling gage instead of gauge. I've historically been in favor of removing superfluous vowels from the language (to wit, the u in colour) but as an armchair etymologist, in this case I'm not on board. Admittedly, there may be some reluctance on my part to breaking a habit, but I think more to the point: there is already a word spelled gage — and to dump all the meanings of gauge into this does the language a disservice. Compare that to colour becoming color, honour becoming honor, etc.; in those cases, there isn't already a word being eclipsed by the shorter spelling, so doing so—in my opinion—is acceptable.

Merriam-Webster defines gage (noun) as "a token of defiance; specifically : a glove or cap cast on the ground to be taken up by an opponent as a pledge of combat" (and by way of side note, is immortalized here by the bard...)

Merriam-Webster goes on to define gauge in the way we currently understand it.

Another definition discovered is:

Gage is (1) a challenge (2) an English plum type, or (3) a variation on gauge. As in "You are the Scarlet Pimpernell, I'll gage!" A gauge is (1) a standard or dimension by which other things are measured, (2) an instrument for measuring something (3) the distance between railroad rails (4) the thickness of the interior space of a shotgun (5) the thickness of wire.

David B. Dubin, PHR
Senior Curriculum Developer
Sage Software

(emphasis mine)

So, gauge it is, and gauge it shall always be (at least here, in regards to the distance between rails, and to a lesser extent, the device that measures this.)