Based on the Moire Method! Many who have used that method know that's its virtually impossible to get any useful or repeatable results. I did not see any acknowledgement of the issues or what he might be doing to solve them.
the folks at Reikan FoCal found so many gotchas in the Nikon and Canon AF systems over the past two years that I'd even put dot tune as a small step above it.
Of course, if your AF system is grossly off, anything that gets it closer will seem to be wonderful.