Hartan Bit Manual page 68

6. To use restraint system: to unlock buckle press in on center button and
pull harness out from each side; to lock buckle, push each side of harness
back into buckle until each clicks in place.
7. To adjust the harness length: See the illustration B for how to shorten and
lengthen the belt straps.
WARNING! Always use the leg straps in combination with the safety belt.
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