I remember when you first posted that image - as I recall that was one of the neighborhood traveling sharpeners, pounds out a pile of kitchen cutlery per stop. Speculated at the time that if your stroke had an arc, and the stone had a matching arc, your edge is essentially flat. You described this gentleman as working the cutlery at a pretty high rate of speed and on a single stone. Once you get the hang of it, is probably a much faster and more natural method for most folks.
+1 :thumbup:
He did have another stone in his kit, a much courser grit to use when reprofiling, but I only saw him use it once in the several sessions that I watched over the years.
One further observation; as a professional, he spent a few minutes on each knife, putting on an excellent 'working' edge. As hobbyists, we might spend 30-60 minutes or longer on each knife, putting on a 'perfect' edge.
Stitchawl