Marathon GSAR Manuel page 11

Rotate bezel counterclockwise, aligning the 12 o'clock bezel
marker with the minute hand to set a starting time.
TIMING BEZEL
1. Rotate your bezel counterclockwise and align the 12 o'clock bezel marker with
the minute hand. This will set your start time.
2. Measure the minute hand against the bezel markers to count the elapsed time.
NOTE: When diving, use your dive watch as a support device alongside the
recommended diving tools suggested by PADI or BSAC.