I used to think the same thing until a few veterans corrected me years ago. Whether there is one T or two T's depends on the amount of tritium lume used on the display (dial, hands, markers, etc.). Now, it makes sense that if only the hands have lume, then one T would be used, but not always. I can't quote you the actual quantity, but there was a line that if the amount went above that limit, two T's were used regardless of where the luminous material was. And yes, tritium lume can get very dark.
I think radium stopped being used in favor of tritium around this period too (early 60's), but maybe a Speedmaster guy can be more definitive about that.
@Spacefruit @gemini4 - can either of you help out on the luminous material switch?
Also, if I were wagering I'd be betting that's an original dial. If not, that's an excellent reproduction of the coat hanger
S from that era.
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