Blimey!

I thought that it was sooner than that, more like 5mm or so, but I can't remember if I've read something in Jim's articles or elsewhere.

I, of course, could me miles off (I often am!).
Now, some of us have mused for years about this and wanting to uncover some more of the springer's innermost secrets, but we really need a see-through cylinder and a camera with 1000 frames per second capability. This would reveal SO much......