FOV in vvvvs transform nodes ( Perspective (Tranform), Vertigo (Transform) ) always refers to the angle between left and right planes of that “perspective pyramid”. Note that it is also the angle between top and bottom planes, since there is no aspect ratio involved in the those nodes.
It is not about the diagonal however…
1 vvvv angle = 1 cycle = 1 Tau = 2 Pi = 360 degree.
things to take care of:
When combining the perspective nodes with aspect ratio nodes you should keep the unifrom scale at 1.0. now it depends on the alignment node which angle (width or height) stays and which angle varies…
in your link the “Focal length multiplier” is quite fuzzy. approximately 1.5-1.6. it’s a pain that focal length ever got a measurement of angles.