The Short Version
The stated dimensions match Miyota's own official technical specifications exactly. The manufacturer's PDF explicitly lists the 0S10 movement at Φ30.8 mm diameter and 4.13 mm height, and two independent third-party technical documents corroborate these figures identically. A small number of lower-authority retail listings cite slightly different measurements (e.g., 30.5 mm, 30.45 mm), but these discrepancies likely reflect differing measurement conventions or listing errors rather than a genuinely different specification.