[allarm]

What’s so difficult with that? Just use pen and paper for calculations, you’re supposed to write down the result anyway. It’s a simple math.

[metaphor]

The goalposts set by the grandparent was reliable mental arithmetic by a notional child:

> ...which probably even children can do in their head reliably.

You're moving the goalposts.

An indefinite number of applications exist where we can make meaningful decisions all day without ever needing to write results down.