yeah, an Abacus is cool, timeless in it's functionality.
also a slide rule is a handy thing, if you can handle it.

Imagine, you are stuck somewhere in Africa, your batteries of your pocket-calc are low,
you have no power-supply for your laptop, but you need to calculate the tubes for an irrigation-system...
you would be glad to have a slide rule...
oh... and have a nice day.