In the GUI Online Help this is explained.
Each view is a visual representation (speedometer) of total Layer 1 traffic. The digital readout shows maximum line rate. The needle shows the actual Layer 1 rate. This data is an aggregate of all ports.
For example,for 4 Gigabit ports – if the line speed for 2 ports is 100 Megabits and the line speed for 2 ports is 10 Megabits the speedometer will be set to 220 Megabits.