… in the right light turns out to be a set of glossy applied steel indices and digits:
This is a Heuer Autavia ref. 3646 with an inner tachymeter scale and a rotating 13h to 24h bezel. A Valjoux cal. 92 movement ticks inside.
The shiny look not seen on any other early Autavia needs a glossy, yet not dressy, strap. This one was made by James Hyman - kudos to James and the enabler @Jarama.