I stumbled across some very interesting material having to do with medieval and earlier navigation that I thought might be of interest to the Topogs. This has to do with the Mariner's Astrolabe which was developed for navigation at sea by Martin Behaim. Master Behaim was a noted geographer of his day, and the personage who is credited with the development of the Mariner's Astrolabe. His statement made in the year 1492,---"Those who navigate this sea must sail with the help of the Astrolabe,"--- was inscribed on a world globe that he created for his native city of Nuremberg which portrayed all the latest and most up-to-date knowledge of the world found by Portuguese mariners to that date.
The Mariner's Astrolabe is an outgrowth of the Islamic "planispheric astrolabe" introduced into Europe with the conquest of Spain in the 10th century. This astrolabe did several things not related to navigation at sea, but on the reverse side it did have the necessary degree scale and sighting alidade necessary for the navigator's use.
I found the information and three models of these instruments at Celestaire (see their on-line catalog under Historical), a company which specializes in various instrumentation including sextants and accessories. They offer cardboard models of the Mariner's Astrolabe, the Planispheric Astrolabe, and a Trilogy of Time Instruments (including a nocturnal (star clock), sundial and perpetual calendar) All these instruments are made from gold covered cardboard and when assembled are working models. The prices are reasonable for the materials and the documentation that comes with them is detailed and with further bibiographic information.
I have purchased the three item set as my Christmas present and I am in the process of building the items. I have to date completed the Mariner's Astrolabe and the three items of the Trilogy. The next project to begin will be the Planispheric Astrolabe, as it is purported to be the most complicated of the set.