both the theory and practice of the astrolabe and many of its variations . One such variation is Gunther ’ s quadrant , which is basically a “ folded ” astrolabe without the star map . I decided that would be a nice first instrument to practice with , so I acquired a sheet of steel from the local hardware store as well as a Dremel hand engraver and started working on it right away . For a first try , I was reasonably happy , except that the engraving machine vibrates too much , even at its lowest setting , and my lines and curves were very jiggly . ( A few years later , I obtained an earlier version of the same machine , with an even lower setting , and was able to make nice lines with it .) Time to move on to the astrolabe . Back to the hardware store . What ? No brass plates ? I thought I ’ d find that easily ! I eventually found a metal distributor who , importantly , mentions on their website they have “ no minimum order ,” and got two 2 mm brass plates from them — one for a mater-tympan combination ( I didn ’ t need seven climates , so just one side of a tympan was enough ; might as well incorporate it in the mater at that point ), and the other for the rete . An important point in the design of an astrolabe is that the thickness of each line will affect the precision of the instrument . When the line is too thick , it is more difficult to