Gamma is the difference between the swashplate tilt angle and the place where the blades finally tilt to thier maximum (and the place where the cyclic stick goes in that direction). In other words, if straight ahead is 0 degrees as a reference, you push the cyclic 2 inches forward = 2'' at 0 degrees. The rotor would be observed tilting about 6 or 7 inches down at 0 degrees (each inch of cyclic might be about 3 degrees of cyclic pitch). The swash plate would have tilted to the right (US convention) a lot to the right and some forward, with the lowest point 18 degrees forwrd of the right side. It is actually hard to find the blade tilt angle, we do it in flight test. If the rotor flaps earlier than the theoretical 90 degrees, then gamma is less than 90. In the case of the 72 (thanks!) degree phase of a robbie, the swash plate actually tilts at that angle