Yes ... Isn't that my point? I meant it as an example of how neither "basic mental maths and ... sanity checks" nor is a calculator with a 0.5% error rate are appropriate.

I mean that it's not a difference of accuracy, it's a difference of domain. A calculator & a slide rule have the same domain, an abacus and Mayan Quipu have the same domain. The calculator & abacus are faster than the slide rule & Quipu. Similarly a typewriter has the same accuracy as handwriting a document (worse if a pencil is used since typewriter's can't easily correct mistakes), but typing took over book writing because it was faster, not because it was more accurate.

I lead with the example of my accountant using a calculator to show it has a different domain than a slide rule, or simple mental techniques.