[Mg-t] Instrument Glasses - Flat, Curved?

[Clive Sherriff]

Here is one I'm quite stumped on.

Some Speedos and Tachos sometimes have flat glass, others convex curved away 
from the instrument dash. I have seen have seen various dials on TA through 
TB, TC and TD that have either a flat or a curved glass.

Similarly for Ammeters, Oil gauges etc.

Were, perhaps pre war flat and post war curved?  were they all curved?  was 
flat original ? etc. etc. (At least I've definately never seen a concave 
one!)

Obviously it's much easier to replace a broken glass with a flat one, and 
cheaper.

So can anyone give a definitive originality view on this please, great 
articles by Doug P and John Marks etc I've seen don't refer to this.

Clive
Oxford, UK
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