DeviceFactor = #Devices * 0.01
LightsFactor = #Lights * 0.05
TriFactor = #Tris * 0.0001
Overall = (DeviceFactor * 3 + LightsFactor * 2 + TriFactor) / 6
Somewhere I found this. Not 100% sure if it is the right one. But something like this I believe.