[ChrisNZ]

That sounds like the right answer - thanks.

I guess it has to be hinged around the plane line as it runs through the point of contact of the ball?

Is that right - remember we are not scared of complexity if it brings out the truth!

Thanks for your help

I think it probably is the point of contact with the ball - but others may think differently, this is just my intuitive thought (which is why I was a bit concerned about getting into this). If this is right, then it's interesting to think that as the plane shifts, so too does the low point line because of this.

I'd be interested in the thoughts of some of the experts on this (although I admit its just a technical/theoretical question which probably has little impact on how you actually hit the ball!)

Chris