I don't think his instruments were really calibrated in the usual sense
of the word. They were just built large enough and sturdy enough that
they could be accurately ruled and and accurately aimed. Most of the
tools were angle-measuring devices to measure angular separations of
stars or stars and planets. Some of them were like sextants that could
measure angular elevation above the horizon. Some had plumb lines to
serve as a vertical reference.
If you build the devices out of stable materials (he used a lot of
brass), make them large enough that the graduations are easy to rule
accurately and also easy to read, mount it in a sturdy fashion, mount
some of them in fixed positions when necessary, plumb some of them when
necessary, etc. then that's all there is to it.
Thus, I would say it wasn't so much accurate "calibration" as it was (1)
good design, (2) large, stable, and accurate "construction". (3)
systematic use.
Here is a site the has descriptions and pictures, including English
translations of how he built the instruments. It was the first hit I go
when I Googled "tycho brahe instruments."
He also needed accurate clocks so he could get elevation data and time
data as objects would transit a fixed line such as the meridian. He
used the sun to determine were the ecliptic was.
I believe one of the biggest improvements over his style of instruments
did not come until Galileo invented the telescope. Brahe used tubes or
double rings or rings and points for aiming. Afer Galileo, the object
sighting could be done with tubes containing lenses and that greatly
improved the accuracy of aiming the instrument at the star being
measured.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
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