Overlays on HP-18C

[rprosperi]

Chary made overlays for many of the financial machines; probably the earliest was the 12C, however since that model was around so long, it's hard to tell. Overlays for the 12C could have been introduced 5 years before the 18C was launched, or 20+ years after the 18C was discontinued...

But I would guess that the 12C versions were first.

Thanks for sharing that Matthias, I've not seen 18C overlays before.