Britax Roundabout 55 Guide D'utilisation page 25

Rear-Facing
When installed in the rear-facing position,
the child seat should be reclined at least
30˚from vertical for children and up to 45˚
from vertical for infants unable to maintain
head and neck control (not to exceed 45˚)
when the car is parked on a level surface.
When installing the seat in rear-facing mode,
recline the seat to position 3 and use the
guide line on the child seat to help achieve
an acceptable recline angle for rear-facing
installations.
Forward-Facing
IMPORTANT: In forward-facing installations, it is important that
the base of the child seat rests completely flat on the vehicle seat.
As illustrated below, it is permissible to allow up to 20% or 7.6 cm
(3 inches) of the base to hang over the edge of the vehicle seat.
Some vehicle seats do not allow enough of the child seat base to
contact the vehicle seat. If this is the case, adjust the recline angle
to a more upright position. Not doing so could cause the child seat
not to perform as intended.
Acceptable overhang
UP TO 3 INCHES
OF OVERHANG
ACCEPTABLE
Child Seat Functions
Unacceptable overhang
OVER 3 INCHES
OF OVERHANG
NOT ACCEPTABLE
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