In this type of graph, we can find the activity of the devices that are selected during the choosen day/shift. As you can see on the screen this is a graphical sample of the devices. It shows you how long was the device moving in a specific time. For example if the device was moving between 6:00 to 7:00 for 30 minutes the percentage will be 50% because it was moving half the time in that hour. Of course you can see all the selected devices you want to see on this graph. The brown dashed line is the median of all the selected devices during the day/shift. the brown filled up space is the median for every last hour for all the selected devices.
As always you can take a closer look by using the time bar below the graph. It helps you to look closer on the specific timeline during the shift or the day.