A scale in this sense is a series of evenly spaced graduations like the marks on a ruler.
Today, we use an End Mill or a Dividing Engine to manufacture the scales.
Scales were used frequently on astrolabes (curved scales) and rulers (straight scales). I have not been able to find out how they did it.
I am looking for first hand accounts or instructions for manufacturing these scales in medieval times. Does anyone know of any such documents?
Note: I asked about medieval technology, because I am most familiar with the history of European manufacturing processes. However, I will happily accept documentation from any preindustrial cultures that did not have the benefit of calibrated lead screws.
Tangentially related post about how measurements were attempted to be kept consistent:
Edit: by u/restricteddata
The short answer would be calipers and dividers.
Calipers, both inside and outside varieties, are quite simple things to make, but they can transfer measurements quite precisely. Likewise, dividers as the name implies could be used to "walk" off divisions of a line or an arc, as well as scribe an arc.
The use of these tools went far past the medieval period. The Starrett Tool company catalog of 1955 listed various kinds of calipers for sale, and clearly there were still plenty of machinists and mechanics who were working by the feel of a pair of calipers when judging the fit of workpieces, parts and general dimensions. And dividers would be used by clockmakers and watchmakers for centuries, to lay out locations for gears , places to drill holes for pivots.
Still, precision was a challenge. The need for greater precision was what inspired the building of the Jantar Mantar in Jaipur: rather than try to make very small, precise graduations on small astronomical instruments, the Rajput king Sawai Jai Singh II made the instruments themselves very big, therefore allowing bigger graduations.
I don't know of any medieval instructions for the actual manufacturing of scales, astrolabes, etc. A medieval craftsman of, say, Nuremberg would be quite reluctant to write up a description of how he did his work, the "art and mystery" of his craft. Those would be very proprietary. The mathematical methods for laying out such devices however did get printed, when printing became possible. You can find the book below here at the Internet Archive
R, T. (1587). A mirror for mathematiques: A golden gem for geometricians: a sure safety for saylers, and an auncient antiquary for astronomers and astrologians. Contayning also an order howe to make an astronomicall instrument, called the astrolab, vvith the vse thereof. Also a playne and most easie instruction for erection of a figure for the 12. houses of the heauens. A work most profitable for all such as are students in astronomie, [and] geometrie, and generally most necessarie for all learners in the mathematicall artes. The contents of which booke yon shall find in the next page. By Robert Tanner Gent. practitioner in astrologie & phisick. Imprinted at London: By I. C[harlewood]. and are to be sold in Paules Churchyard, by Richard Watkins.