A level 1 incremental backup can be either of the following types:
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;
Sunday
An incremental level 0 backup backs up all blocks that have ever been in use in this database.
Monday - Saturday
On each day from Monday through Saturday, a differential incremental level 1 backup backs up all blocks that have changed since the most recent incremental backup at level 1 or 0. So, the Monday backup copies blocks changed since Sunday level 0 backup, the Tuesday backup copies blocks changed since the Monday level 1 backup, and so forth.
The cycle is repeated for the next week.
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0
BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE; # blocks changed since level 0
Sunday
An incremental level 0 backup backs up all blocks that have ever been in use in this database.
Monday - Saturday
A cumulative incremental level 1 backup copies all blocks changed since the most recent level 0 backup. Because the most recent level 0 backup was created on Sunday, the level 1 backup on each day Monday through Saturday backs up all blocks changed since the Sunday backup.
The cycle is repeated for the next week.