Sinn refers to this as their “Navigation Chronograph” model, and it features traditional aircraft markings on an internal rotating bezel. The 903 Classic and H4 use the hand winding Lemania 1883 movement with four subdials including moon phase indicator, while the rest use an automatic Sellita SW 510 movement with subdials at 3, 6, and 9. All feature an extra crown on the left side of the case to turn the inner bezel, though this is at 10 00 in the SW 510 models and 8 00 for Lemania versions.
All versions feature a 41 mm case with traditional “twisted” lugs. The case is 13.2 mm thick for Lemania-based models and 14.5 mm thick for SW 510 models. All feature sapphire crystal on the front and display caseback.