IWC Schaffhausen BIG PILOT'S HERITAGE 55 Mode D'emploi page 22

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U S I N G T H E A N T I - L O S S S T R A P
So that the watch with the XL strap can be worn both over and
under the pilot's jacket, the anti-loss strap is perforated for the pin
buckle along its entire length. If you want to wear your Big Pilot's
Heritage Watch 55 against your wrist, you can loop the end of the
strap as suggested in the sketch.
B I G P I L O T ' S H E R I T A G E W A T C H 5 5