Those people were really artists improving their products and their tools at every step and their heritage is still alive today.
The watchmaking/clockmaking industry trained a whole generation of precision machinists which led to a revolution in mechanics, toys, calculating machines and ultimately set the stage for worldwide navigation and the industrial revolution.
https://en.wikipedia.org/wiki/Curta
I've never been able to find one that I could afford though.
I don't know which precision a not electronically assisted telescope have, but it's sure it's impressive.
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.
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.