Britax safe-n-sound BS4000A-020133 Manual Instructions For Installation & Use page 22

HOW TO USE
WARNING:
A SASH BELT UNDER THE ARM OR
BEHIND THE BACK IS DANGEROUS.
SEATBELT
UNDER THE ARM
IS DANGEROUS
Seat belt fitting closely
across the chest and
through the sash guide.
Lap belt must always be
firm on the thighs.
The child should not
slump or slouch.
NOTE: Seatbelt extenders should not be used if the seatbelt is not long
enough to fit around the child. If a seatbelt extender is used then the seatbelt
buckle must not be in contact with the child.
22
Instructions for Installation & Use - Series No. BS4000A-020133
SEATBELT BEHIND
THE BACK
IS DANGEROUS