How old is the segmented digit display?

[Peter Klein]

The HP-41 series used a 14-segment display. That seems to be the minimum for display of all Latin letters and Arabic numerals. Fourteen segments can display all upper and lower case Latin letters with the exception of lower case "s." With a 7- or 9-segment display, you have to mix cases. And some letters are impossible in either case, unless you fudge a few. That "fudging" may be acceptable to people like us, but probably not to the general public.

The Wikipedia article on the 7-segment display,
https://en.wikipedia.org/wiki/Seven-segment_display
contains a chart showing how each letter and number is constructed. Under "See also" at the end of the article, there are links for the other display types with more segments.

If we don't care about which letter case we use, the seven segment display can show all numbers, including hex digits A-F. But letters K, M, V, W and X are missing. And G, S, and Z are can be confused with similar-looking numbers. 9 segments is better, but still doesn't cover everything.

14 segments is probably good enough for most purposes, but even it misses some punctuation marks like double quotes. 16 or 22 segments are better, but probably don't pass the cost-benefits analysis. I suspect that's why they weren't widely used. Once we have enough memory and processing power, it is often better to use a dot matrix display if you want to show any possible character, This decreases readability on lower resolution displays, but assures that one can show any character properly.

I find the 7-segment numeric displays of the Voyager series to be the most readable of all the HP LCD models. I also like very much the lower (numeric) half of the HP 30B (repurposed as a WP-34s). In comparison, the dot matrix numeric displays of the HP-32s, 32sii and 33s are good, but not as pleasing to my eye. The all-dot matrix display of the 42s does the job, but I don't like it so much because of its small character size and finicky contrast. The DM32 and DM42 have a high-resolution dot matrix display where where we can have highly readable alphanumeric characters.

Consider the HP 30B, which was repurposed for the WP-34s. It uses a 7-segment display for the main number display (lower part), and a dot matrix display for the upper part. I can almost hear the discussions that went on between the engineers, bean counters, usability experts and marketing types. They came up with a compromise that was good enough for a business calculator, and acceptable but not ideal for the "do absolutely everything" WP-34s. The numbers are very readable. The alpha characters are reasonably so, but we might grumble about them.

The history of calculator displays is a classic case of compromises between what needs to be displayed, current technology, cost, readability, and how much the intended audience will accept the compromises. If you have a WP-34s, type h X.FCN, scroll to WHO and XEQ it. You will see a wonderful example of exactly such a compromise, as the names display both in dot matrix and then 7-segments.