POD reads: C<$chargeable_units> is the number of chargeable units (days between start and end dates, Calendar adjusted where needed, minus any applicable grace period, or hours) But actually it looks like the grace period (firstremind) is still included. Otherwise this would make no sense: my $chargeable_units = get_chargeable_units($fine_unit, $start_date, $end_date, $branchcode); my $units_minus_grace = $chargeable_units - ($issuing_rule->{firstremind} || 0); my $units = C4::Context->preference('FinesIncludeGracePeriod') ? $chargeable_units : $units_minus_grace;