HP B6960-96035 - Manual (Page 94)

Incr A simple incremental backup, shown in Figure
23 on page 95, is based on the last backup that is still
protected, which can be a full backup or an incremental
backup.
Incr1-9 A leveled incremental backup, shown in Figure
24 on page 95, depends on the last backup of the next lower
level that is still protected. For example, an Incr1 backup
saves all changes since the last full backup, while an Incr5
backup saves all changes since the last Incr4 backup. An
Incr1-9 backup never references an existing Incr backup.
Planning your backup strategy 94