Calculators you regret buying?

[Johnh]

I used to regret having an early-model Sinclair Scientific. It was cool in the playground at age 15, but didn't really have enough to make it useful, even for high school maths. Too slow and not accurate enough compared even to a slide rule!

But what a marvel of squeezing into a pint pot! I do appreciate it now and it taught me to think RPN, which I've retained for 50 years even without an HP until recent times.