The July 22 cover, “Sticker shock,” and the related article say that the powerful forces that arise at the surface of micromachines weren’t expected. Any skilled machinist who has used Johannsen gauge blocks in measuring and checking his work would not be surprised at all. These blocks are stacks of hardened steel rectangles with highly polished, flat, parallel surfaces. They are used in the gauging of measurements in precision machining. Because of the precise finish and flatness of the pieces, molecular cohesion forces hold them together in a bond not easily broken. Johannsen gauge blocks have been in use for a hundred years.

Norman MacRitchie
Honolulu, Hawaii