The second chapter presents findings emerged from the investigation of the artifactual sources and which could be sensed only in textual sources. This astrolabe gives us an idea on how these instruments looked when they came into Islamic civilization in the 8th century. The further development of Islamic astrolabe-making is documented in chapter three by showing various examples. The Islamic pieces of the 10th and 11th centuries already exemplify exceptional progress both in Islamic astrolabe-making and makers sophistication. Chapters four and five outline characteristics which allow to distinguish European astrolabes, and which also allow a discrimination in several traditions.
European astrolabes lack a consistently high quality in the nomogrammes for centuries.
Some of the European astrolabes demonstrate a high level of mechanical and astronomical skill, whereas other instruments that demonstrate a equivalent quality in workmanship, illustrate an elementary astronomical incomprehension of their creators. This reflects the different level of delivery of astronomical knowledge in Europe and the incompleteness in the transmission of knowledge from medieval Islamic world to Europe. A hindrance in the evaluation of preserved European instruments is the missing signatures and dates which seems to have come common in Europe first about 1450. A reasonable argumentation for dating the undated European pieces now as before seems questionable. The instruments could be combined in traditions but no time-limit for a tradition is given here as necessary further investigations of other stylistic elements could not be conducted in the course of this thesis.