Rule Signed Antonius Braun

This small brass rule has two linear scales, one labeled "4" that is divided to quarter-units and numbered by ones from 30 to zero, and one labeled "3" that is divided to quarter-units and numbered by ones from 22 to zero. The units are 0.5 cm (7/32") and 0.7 cm (9/32") long, respectively. A brass peg is in the center of the rule, and a small round hole is on the right edge. These suggest the rule was designed to attach to other rules, although no such rules were received with the instrument.

While the scales are in a 4:3 proportion to each other, the pre-metric units of measurement represented by either scale are not known. The length of the divided portion (15.6 cm or 6-3/16") is almost exactly half the length of the average fuss (31.4 cm or 12.36"), a traditional "foot" measure used in German-speaking areas of Central Europe.

The top edge of the rule is marked: Antonius Braun Invenit et Fecit 1722. Anton Braun (1685–1728), a native of Swabia in southwest Germany, made instruments in Prague by 1720 and in Vienna by 1724. In 1727 he built a pinwheel calculator during a competition to become chief instrument maker for Holy Roman Emperor Karl VI.

References: Herbert Arthur Klein, The Science of Measurement: A Historical Survey (reprint; New York: Dover, 1988), 63; Russ Rowlett, How Many? A Dictionary of Units of Measurement, July 11, 2005, http://www.unc.edu/~rowlett/units/index.html; Adler Planetarium, Webster Signature Database, http://historydb.adlerplanetarium.org/signatures/.

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