Just wanted to mention one of my other vices.....vintage slide rules. I have a small collection of them dating from the 1930's till their very end in the early 1970's. I got a few from older engineers I worked with over the years and many come from eBay, estate sales and flea markets.
I'm always looking for ones I don't have and would either buy them or trade strops, etc....
On a more modern note I also have a few old Texas Instruments red LED scientific calculators.

Anyone here ever use these in the past?

Tony