How old is the segmented digit display?

[Johnh]

Really interesting to see that the concepts for these displays were in place so early last century! There's something really clear about a good 7-segment display for displaying numbers, better than most dot matrix or more complex versions, up until you can do a really bright high-def display. Also, those 7 segments need minimal electronics to manage. Just for our calculators, the 7-segments look the best for when only digits are needed.

Sadly, when you try to make them do letters too, there are several letters that just don't have a very credible option, even if a mix of upper and lower case is accepted. M, Q, V, W, X seem the trickiest. So a puzzle that I sometimes play with is, what is the simplest addition of another segment or two on a 7 segment display, that preserves the clarity, but gives an intuitive reading of letters too? Is it as on an HP41 for example?