While yes, "Astronomical work also required precise computations, and, in 19th-century Germany, a steel slide rule about two meters long was used at one observatory. It had a microscope attached, giving it accuracy to six decimal places" (same Wikipedia page), remember that this thread is about calculating devices one might carry in one's pocket, have on one's self, or otherwise be able to "grab".
(There's a scene in a pre-WWII SF story where the astrogators on a large interstellar FTL spacecraft use a multi-meter long slide rule with a microscope to read the vernier scale. I can't remember the story.)
My experience is that I can easily get two digits, but while I'm close to the full three digits, I rarely achieve it, so I wouldn't say you get three decimal digits from a slide rule of the sort I thought was relevant.
> With the ordinary slide rule, the accuracy obtainable will largely depend upon the precision of the scale spacings, the length of the rule, the speed of working, and the aptitude of the operator. With the lower scales it is generally assumed that the readings are accurate to within 0.5 per cent. ; but with a smooth-working slide the practised user can work to within 0.25 per cent
That's between 2 and 3 digits. You wouldn't do your bookkeeping with it.
https://en.wiktionary.org/wiki/couple - "(informal) a small number"
FWIW, "Maximum accuracy for standard linear slide rules is about three decimal significant digits" - https://en.wikipedia.org/wiki/Slide_rule
While yes, "Astronomical work also required precise computations, and, in 19th-century Germany, a steel slide rule about two meters long was used at one observatory. It had a microscope attached, giving it accuracy to six decimal places" (same Wikipedia page), remember that this thread is about calculating devices one might carry in one's pocket, have on one's self, or otherwise be able to "grab".
(There's a scene in a pre-WWII SF story where the astrogators on a large interstellar FTL spacecraft use a multi-meter long slide rule with a microscope to read the vernier scale. I can't remember the story.)
My experience is that I can easily get two digits, but while I'm close to the full three digits, I rarely achieve it, so I wouldn't say you get three decimal digits from a slide rule of the sort I thought was relevant.
I'm a novice at slide rules, so to double-check I consulted archive.org and found "The slide rule: a practical manual" at https://archive.org/details/sliderulepractic00pickrich/page/...
> With the ordinary slide rule, the accuracy obtainable will largely depend upon the precision of the scale spacings, the length of the rule, the speed of working, and the aptitude of the operator. With the lower scales it is generally assumed that the readings are accurate to within 0.5 per cent. ; but with a smooth-working slide the practised user can work to within 0.25 per cent
That's between 2 and 3 digits. You wouldn't do your bookkeeping with it.