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My calculator was very special, as was my relationship with it. You can read about it if you like.

Back in 1975 or so, it could do something no other model could do at the time. Beside the digits from 0 to 9, there was a trick to make it display six more characters, including an upside-down 'u' and a blank space. I don't know this for a fact, but it's pretty apparent that my calculator's chip used hexadecimal internally, though it (usually) only displayed the usual ten digits. But it had a MR button that did a 'Memory Recall'. It would recall the number that had been in the display before the last operation you performed, something like an early version of the 'undo' function found in many modern text editors and other programs. A "traditional" calculator loses its memory when you turn it off, so if you hit this key right after powering the calculator on, there is nothing to recall; what you see are the un-initialized contents of the "recall register". In my calculator, this happened to be a sequence of eight of the otherwise never-visible digits.

I found that I could do some limited arithmetic with these digits which could be used to "generate" the other five kinds of digits (as well as all the "ordinary" digits, of course). And so it came that I was the only kid on my school bus (and probably for many miles around) that could make his calculator spell things like

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