A change in policy requires a complete backup of the accounting server every seven days...

A differential backup is a type of backup that copies all the files that have changed since the last full backup. A differential backup requires more storage space than an incremental backup, which only copies the files that have changed since the last backup of any type, but it also requires less time to restore in case of data loss. By combining a full, weekly backup with daily differential backups, the administrator can ensure that only two backup sets are needed to restore a full backup as quickly as possible. Verified References: [Incremental vs Differential Backup]