Buick 1998 Century Owner's Manual page 61

A rear-facing infant restraint (B) positions an
infant
to face the rear of the vehicle. Rear-facing infant
restraints
are
designed for infants of up to about
20 lbs. (9 kg) and about one year of age. This type of
restraint faces the rear so that the infant's head, neck
and body can have the support they need in a crash.
Some infant seats come in two parts
--
the base stays
secured in the vehicle and the seat part is removable.
1-53