[TR] TR3A overheating

[Randall]

> but in the absence of such a tool is this 
> gauge really calibrated with smaller increments before 185 
> than after? Or is anything before 185 just  filling up space 
> on the gauge face and doesn't mean anything?

I believe the answer lies somewhere between those two extremes, David.
After half a century of service, it's doubtful whether any of the marks mean
anything ... but the gauge mechanism is "non linear" which means that the
original marked points were approximately correct.  (Very approximately,
because these were never high precision gauges even when they were new and I
suspect the markings were chosen as much for visual appeal as accuracy.)

But the "increment" doesn't suddenly change in the middle of the dial.
Instead they get progressively smaller across the dial.  So that mark above
185 is hypothetically somewhat closer to 215.  (Note that 185 is roughly 2/3
from 90 to 230; and 215 is roughly 2/3 from 185 to 230.)

BTW, even those "laser pointer jobs" leave a lot to be desired in terms of
accuracy.  For one thing, they assume that all objects glow the same (in
infrared light) and it's not true.
http://www.openxtra.co.uk/articles/emissivity_intro.php

Randall