trying to understand lens value

I’m trying to understand the lens value of the camera so I can get this export script working. I need to somehow figure out what, if anything, the lens value has to do with focaldistance, lensradius, and FOV.

From the manual:

Lens - the number is derived from the lens values of a photo camera: 120 is telephoto, 50 is normal, 28 is wide angle.

Can someone point me in a direction to better understand these numbers?

thanks,
ben