[Mathew]

Vertical planes relative to the inclined plane. This is just a random thought again and may not be totally accurate...

A constant - The vertical plane of any hinge action will go directly through at 90 degrees to the inclined plane and when the blade of the hinge is at 0 (low point) and 180 degrees.

However the rest of the time - horizontal will turn the lever assembly the closer it gets to 90 degrees and then rolls back again until 180....vertical the exact opposite. Angled however maintains the same 90 degree constant throughout regardless of where it is on plane....