So what exactly are the differences between this Speedmaster Reduced and a Speedmaster Professional? Moonwatch versus ReducedLet me start by writing that the now-discontinued Speedmaster Reduced is still often mistaken for the popular Speedmaster Professional Moonwatch. Omega Speedmaster 3510.50Throughout this article, you can find images of the Speedmaster Professional Moonwatch and the Speedmaster Reduced to compare. While the Speedmaster Professional measures 42mm in diameter (and 40mm across the bezel), the Speedmaster Reduced is smaller at just 38.5mm. With the Speedmaster Reduced, it lands on 44.5mm, while the Speedmaster Professional measures slightly over 47mm.