Union Glashuette U 7751 A Gebrauchsanleitung Seite 15

Use
Chronograph function
Press the Start/Stop push-button (12) to start the
chronograph. Press the Start/Stop push-button (12)
again to stop it. The chronograph will resume if the
Start/Stop push-button (12) is pressed again (added
times), or the three chronograph hands (9, 10 and 11)
will return to zero if push-button (13) is pressed.
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