‘Si te omnimoda delectat precisio’: early astronomical instruments with scales and the multiple meanings of precision in the sixteenth century (Q6553077)

The article deals with 15th--16th-century ways of dealing with ``precision'' and ``accuracy'' -- defined respectively (Note 2) as ``a measure of the scattering error of various measurement values under the same conditions'' and ``a measure of how close a measured value is to the true value'', in part in the construction of measuring devices (astrolabes, equatoria, armillary spheres), in part in written works dealing with the use of scales.\N\NAs it turns out, it is only with Tycho that the terms are used as we would expect. Earlier writers might give detailed prescriptions of how to add precision to scale readings that compensate for the deviation of the tropical year from 365 days; for the ``rotation of the eighth sphere'' (now, precession); and even for the changing obliquity of the ecliptic -- all negligible compared to what could be read on the scales of the instruments, and in the author's opinion used as a pedagogical ``reminder about the subtlety of the full theory that accounts for minute differences and motions'' (p. 42).\N\NSeveral sophisticated instruments and a number of ways to improve the precision of the reading of scales are discussed.