Guest Disk Free Space chart unclear meaning

[lucaliga]

Hello,
Veeam ONE 9.5.0.3201. Using Veeam ONE Reporter - VMware Overview - Guest Disk Free Space then drill-down a VM. The section show the chart of the disks usage trend but for every disk shows three lines.
See the image https://pasteboard.co/H8NtKoS.jpg for the disk E (which has size 700GB).
The chart show one line starting at 700 remaining the same size during the period, one line starting at 600 with variations and a line starting about at 550 with a little grow. If the reports has to show the trend of used space growth, that is one variable, then there should be one line per disk. I dont understand the meaning of many lines per disk ?

Many thanks.

[Shestakov]

Hello.
Upper line is disk capacity, curvy line is history of space usage and straight line is the space usage trend.
Thanks!