0 a device used outside, especially in the past, that consists of a thin piece of metal attached to a flat surface printed with numbers. It shows the time by the metal making a shadow on the surface as the sun moves across the sky. -- 日晷，日规
The other topics include the education of architects, technical devices like sundials and water clocks, mechanical devices for war, and the ethnography of various peoples.
Then he learned to draw the various designs of sundials, indicating the hours exactly, and to measure the height of objects by geometric rule.
He also mentioned how to apply this method in surveys and how to expand the principles of the gnomon to make sundials.
A sundial is a wholly unreliable method of measuring time, and so is a clock.
Improved communications and better clocks revealed another problem with using a sundial as a clock.
Then, what is to happen to the sundials?
He asked for a miracle, and it was suggested that the shadow might go backwards over the sundial for a considerable number of hours.
They are trying to judge it with a sundial set the wrong way round.
