Hi!
My wife just (to be honest: it was 10 minutes ago) told me without obvious reason: "You know, what is your most useful gift ever? The hp-calculator! And what else? I wouldn't exchange it for any of your other calculators!"
This is an hp-21s (stat-math) that I bought her for christmas long ago, must have been 1985 or '86, we were still at university then and it was the most expensive one I could afford. She has been using it ever since (over 20 years now, hard to believe how time goes by) and prefers it over Excel when calculating the average marks of her students and for similar tasks that teachers have to do.
By the way: It runs on its second set of batteries, not only voyagers have low power consumtion!
Greetings, Max