differential backup device type

Hi

I want to make a weekly differential  backup
I defined 1 Mediapool Overwrite Protection Time 1 Week, Append Time 4 Days

&

first  Job with Options set to Full Backup and Overwrite on weekend
2nd Job with Options set to Differential and Append

I do not know whether to create only 1 backup device for the 2 jobs , or create 2 backup device one to each of the two job

regards

Sharon