Ptolemy wrote the Planetary Hypotheses for both astronomers and instrument-makers. Most studies of this text concentrate on its meaning for the former, but there remain many questions surrounding its meaning for the latter.1 This article investigates the purpose of Ptolemy’s Planetary Hypotheses in light of what he says about instrument-making. It takes up the following questions: what kind of instrument does Ptolemy describe? And, could such an instrument have been constructed? I argue that he did not have one specific design (...) in mind, but instead he offered craftsmen options for the content, design, and operational methods. In addition to exhibiting his astronomical models and estimating planetary positions, the... (shrink)