You've got it at last Chopjock, that is a perfect demonstration of a class 1 profile (it wasn't called that then). From the hover the pilot flying accelerates the aircraft and the pilot monitoring calls 'groundspeed' when he sees the ground moving past the window and then 'airspeed' when the ASI just begins to fluctuate. At that point, the pilot flying adjusts the attitude and power to climb almost vertically whereupon the pilot monitoring calls '20 feet', '40 feet' and 'rotate' as the radalt shows 50'. At that point, the pilot flying initiates a further acceleration and is committed to fly away - before this point, in the event of an engine failure (or other emergency) the take off is rejected.
This profile allows the S61 to depart from a very short runway providing class 1 performance in the same way that the vertical profile provides. It does not allow a departure with obstructions that would be found in a stadium environment!
Cheers
TeeS