I searched for ancient arabic calendars and for "التقويم العربي القديم" it was futile. But I figured out, that calendar scales went on the edge of astrolabe, because around this image it was said: Calendar scales (round the outside edge) on an Islamic astrolabe, Photo Credit: artselectronic.wordpress.com.
Heres’a an astrolabe, but it contains 72 letters on its edge, some repeat but in the system I don’t understand, yet:
Here’s a similar astrolabet, hm, astrolabe, only it’s edge is, even though also of 72, is somewhat different:
72 is 360 divided in 5, as this another astrolabe demonstrates: