[marknorton]

The value of the infinity stop is that it is the only focussing reference there is - irrespective of whether you ever focus there. It should be right so that the complete focussing characterstic back to 0.7 or 1.0 metres can use it as a base reference.

Even with infinity set and even with close focus set, focussing in between relies on the profile of a cam in the camera and the profile of a cam in the lens - look at older style lenses like the Noticlux, pre-ASPH 50mm Summilux and you can see how the brass cam has been custom ground to calibrate the lens to an established standard.

It's an untidy solution because this whole system of proxy focussing - where you are relying on one system to tell you whether or not another is in focus - is prone to error and the problem will only go away when the Leica M is able to sense and feed back to the user real focus, not some "if-your-camera-and-lens-are-correctly-aligned-it-should-be-OK" alternative.