What do you base that on? I thought some industrial applications actually required much finer tolerances. Things like telescope mirrors. It probably depends on what you consider to be a mechanical tool.
-That would be pretty good watches - the requirement for being labelled a chronometer by the Swiss is +6/-4/day (with some further requirements - positions and temperatures)
Seiko tune their top-of-the-line Grand Seikos a bit tighter - +5/-3/24h.
They also have some limited edition VFA (if memory serves - Very Fine Adjusted) watches capable of +/-2s/24h.
The engineer in me finds this kind of accuracy in a mechanical device just a hair short of black magic.
>The engineer in me finds this kind of accuracy in a mechanical device just a hair short of black magic.
I'm curious where you get this intuition. As an engineer with a background fully in electronics/software my intuition is that multiple-seconds per day of error is horrible. I never got into mechanical watches because of this. There are so many great quartz based watches that keep time so well that I've never seen the allure of the mechanical. I'm now curious from this discussion how big of a feat it is anyway but have no intuition for it.
https://en.wikipedia.org/wiki/Curta
I've never been able to find one that I could afford though.