This calibre has a distinctly different rotor with much less material removed around the Omega logo, the calibre number “1158” engraved at the bottom, and a 21K solid gold weight added.

While this movement appears to be very similar to the Cal 1158 with only a different rotor, the differences are far more significant.

The Calibre 1158 features a different main plate, wheel train and automatic winding bridges, balance and barrel bridge, barrel, and even a different regulator.  On the specifications front, the biggest difference is that Calibre 1158 is a COSC certified chronometer, where the former two calibres were not.