It hasn't been restored in the time I've come to know the gauge, but I suspect its been very well polished a couple of times by the current owner. I'll speak with him on Wednesday when I see him to see if he can send me some better photos of it. I must say though, for NYABco. to have collaborated with Ashton to make a gauge with this pressure range and a single needle, I believe it points to a steam jamb break system.

This is the system that the three Baldwin locomotives with steam brakes featured. Does any of this clearly indicate NYABco.?

Here an example for a Baldwin with NY air brakes.
2-6-2 Oregon-American Lumber #105
including the info from Baldwin factory ledger.

The third pic show a closeup of the NYAB LT-5 Duplex Compressor.

The last pic show Baldwin
2-6-2 City Of Seattle #6 closeup with Westinghouse 8 1/2" Cross Compound Compressor
identical twin with the exception using Westinghouse air brakes.

Surprisingly both locomotives survives today.
Can you name where they are?

Denmark gets interesting here. The gauge certainly seems to belong to a steam brake. Is it possible that the loco concerned would have had vacuum brakes for the train? Or do you think steam brake only?

That would be interesting as locomotives with vacuum brake / steam brake were mostly a British thing - elsewhere in Europe where vacuum brakes were used they were generally used for the whole train including the loco.

The other odd thing about Denmark is units of measurement, the drivers instructions say that the working vacuum should be 0.65 kg/cm^2. Elsewhere in Europe, with vacuum brake systems made in Austria, Germany or UK, it was normal to measure in cm of mercury (or inches for UK). Which makes me wonder if much early vacuum brake equipment in Denmark might have come from USA.

"Vacuum" is simply the absence of atmospheric pressure; think about the difference between psig and psia in steam measurements. You could easily have "200psi of vacuum" -- on Venus, or at the bottom of the Mariana Trench, where the equalized ambient atmospheric pressure was 200psi or greater. But at sea level or greater... no, any more than you can have the thousands of negative degrees of temperature that produce flash-freezing in bad science fiction movies.

I tend to like the idea of bar as a pressure measurement that both metric and English users can find a convenient unit -- one standard atmospheric pressure, not quite 14.7psi, not quite 760mm Hg, not some idiot number of pascals to get confused. Those of you who know SI will appreciate the weirdness of measuring pressure in kg/cm^2, although those are reasonable units proportionally in metric.

If you want more precision in English units, converting from bar, than modulo 14.7, any number of decimals will give it to you.

My impression is that's a main reservoir pressure gauge for an air system. It seems unlikely that that range of pressure would be applied as a straight independent steam brake, but I have no experience with what 'period' equipment would use... and that brings up why NYAB would provide a branded version of an Ashton gauge for any use except something like a steam independent. I doubt there was much use of exhausters and vacuum independent brakes on steam locomotives that used an Eames-style train brake -- but again, there are historians of that period that know more and better than I do.

Industrial and logging lines used steam brakes right up through their demise - not the big operators, of course, but those shifting light cars with no brakes on them. I have yet to see a lokie with a steam jam that had a pressure reducing valve combined with the brake valve, but all I've laid hands on had a drain valve opened by a spring at the lowest point in the system. Steam pressure closed it when making an application, upon release blew out condensation.

Dave, would an engineer using a steam brake need a separate valve to know how much pressure he had on a straight independent? Wouldn't it be more obvious just by feel?

Not on slow industrial lines, but if anybody is still using them on mainlines it could be useful, perhaps..... I don't know any experienced engineers who look at the pressure gauge when using the air independent brake either, come to think of it. Jams are jams.