Not many people know this, but in the atom bomb is a PMV-11 iron so well-sharpened that when the bomb hits the ground it splits an atom. Einstein used waterstones at 1,000,000 grit to achieve this. This photo shows Einstein calculating the bevel angle with and without the ruler trick. The bottom right calculation is believed to be the true grit of Lee Valley's green chromium oxide. Sadly, he died before finishing that part of the equation, and it seems we will never really know.
Attachment 352289