I must admit this one was not necessary for either my work or leisure... But having so much brains in such a little piece was astounding and I decided to pour money in it.

I did the foolish thing to exchange it for... a Psion II. The friend who had it was stolen in the airport, along with his case, laptop and everything...

So I bought another one, just to remember my first days programming when at Tandy Radio Shack, back in the 80's.
HP 16C

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The Museum of HP Calculators