Job-Log Summary: What is the difference between Byte and scanned Bytes?

Hi,

when I look into the job history (in that case a Backup of VM's via VMware Agent into a Dedup-Device) I found two entries:

Byte:  321.147.088.814 Byte

and

Number of scanned Byte: 297.140.302.848 Byte

Why are these two values different and what is meant which each value?

Used Version: Backup Exec 2012 SP1, actual patch-level

Thanks in advance.