OGVI (OLCI Global Vegetation Index)

Hello Marco, I would like to know how is obtenied OGVI (OLCI Global Vegetation Index). I understand that O3, O10 and 017 bands are used, but specifically how? I would need to know the algorithm. Thank you very much

All I know is this:

Can someone give some more explanation on the scale_factor of OGVI?
Why is it 0.003937008 ?
With a scale_factor of 0.004, DN [0, 250] would result in physical values [0.0,1.0] (the physical range of fAPAR).
Now a DN of 250 results in OGVI = 0.984252, DN of 255 results in OGVI = 1.00393704.

Thanks for your help!