Diono Monterey 2XT Manuel D'instructions page 30

USING THE SHOULDER BELT GUIDE STRAP
WARNING! When in backless mode, if the vehicle
shoulder belt does not correctly fit the child, then the
seat must be used with the shoulder belt guide strap or
with the backrest attached and properly adjusted to fit
the child.
1. Remove shoulder belt guide strap from
storage area underneath seat.
2. Position child correctly in seat,
making sure lap and shoulder belts are
positioned properly across child.
3. Attach the
strap onto the diagonal shoulder belt.
4. Adjust strap to correct length,
so that the
above shoulder.
30
BACKLESS BOOSTER
RED shoulder belt guide
RED guide is just