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I am very thankful to the list member who sent
this reference for the Armillary spheres:
http://www.hps.cam.ac.uk/starry/armillobser.html
I am terribly sorry, that I could not recover this
person's name and his message.
(How the search engine works on this list archive is
far beyond my understanding:-(
Maybe someone more experienced could explain!!?
The "Observational Armillary sphere" on this site
seems to be an "analog copmuter" (as I conjectured before)
with which you can do the same
tasks as with a Star Globe.
(or Wulff grid, or planispheric astrolabe).
The only difference is that the Star Globe has fewer graduated
circles.
(Namely, 4. The modern Freiberger version has only 1 or 2
circles, but permits to solve the same problems.)
Mathematically, all devices solve a spherical triangle.
(I suppose with 1/2 degree precision).
Some of them also include some "almanac data", mostly
star positions.
Alex.
