Most Islamic geometric star patterns can be derived from tilings of regular polygons, and often additional non-regular polygons are needed, especially in designs based on pentagons/decagons. Generally the angular relationships between the polygons are exact, but there are a few examples, mainly Mamluk with a few from the Seljuk Sultanate of Rum, that depend on approximations. Variations in the additional interstitial polygons accommodate the inaccuracies. Many more such possibilities exist, and a fairly simple spreadsheet technique allows for their investigation.