: Mark, thank you for this helpful information – I never stop
: learning! I always assumed that only the early (eggshell)
: Carrera 3647/2447 S had "non-T-dials". Gary's non-T
: 3647 S with s/n 65XXX has the starburst dial.

: Robert

Yes, it's relatively late but the NRC in the US only codified the tritium markings in 1966 and the US was one of the early adopters of the legislation, other jurisdictions held out a bit longer. ISO 3157 is the international standard for lume in watches if you want to read more - I find it quite an interesting field.

Given the half life of H3 is just over 12 years, if you have a watch from that first run of Carreras and the lume is intact, it will now have less than 5% of the tritium that it originally had. Even if the ZnS phosphor base material is still intact, it's unlikely to be triggered enough for the watch to glow enough to show - nonetheless there will still be the odd decay event going on in there.