a big watch...

[Yazo]

Originally Posted by Dan Pierce

It's an ETA movement with a chrono module installed on top [or underneath] to the base movement rather than an integrated chrono movement like the Valjoux 7750 or Zenith.
The chrono gears are working even when the chrono function is not running, adding premature wear. The module requires special tools and most modules are just replaced instead of repaired.
dP

Thanks for that tidbit Dan!