Abaci would actually probably be good for making mental math come naturally.

As a general rule, i am on team - if you need a calculator in math class then you aren't learning math.

Because if you're studying real math, a calculator wouldn't help?

Pretty much. You either do every calculation symbolically, or you need a full-blown computer for numeric methods.

Either that, or you are trying to teach people arithmatic, in which case having them do it by hand is a benefit.

We learned to use them in elementary school (1970s)!

It was what I think they now call a "manipulative" as way to teach place value, addition, and multiplication.

An interesting question, actually. It feels like they can be a good teaching tool, compared to calculators.

"You won't always have an abacus in your pocket."