mm diameter disk, which will tell the time the world over. They say it is capable of two minutes' accuracy ("Good one"). They say, too, that it requires a working knowledge of sundial principles. But then, doesn't one need a working knowledge of a wall clock? OBSERVATION: I myself had a single paper published in the field of gnomonics (sundials), at Yale. It described an accurate sundial one could wear on the wrist: a serious piece, not a miniaturised garden dial. How I wish someone could put it into production.