...doesn't have to be high tech. I've got a new toy that I really like:

It's a Aristo 868 slide rule, and I find it pretty amazing how much you can do with it. Best of all: no batteries :-)

I'm obviously not against high tech, for example:

That's my trusty HP 28S, which I got in 1988 - RPN forever! But still there is a certain minimalistic appeal to the simple magic of sliding log scales...