This is a school project I wrote a few years ago, on using 3D Computer Graphics. It explores a phenomenon whereby a sundial can actually go backwards in the tropics!
Understanding spherical astronomy requires good spatial visualization. Unfortunately, it is very hard to make good three dimensional (3D) illustrations and many illustrations from standard textbooks are in fact incorrect. There are many programs that can be used to create illustrations, but in this report we have focused on TEX-friendly, free programs. We have compared MetaPost, PSTricks, Asymptote and Sketch by creating a series of illustrations related to the problem of why sundials sometimes go backwards in the tropics.
See also paper by Sun Yifan: Using 3D Graphics to Explain Why a Sundial Can Go Backwards in the Tropics
In it, the Hezekiah Phenomenon is being discussed.
Quote: First, we would like to explain where the name Hezekiah Phenomenon comes from. In the Bible there is a story about God making the shadow of the sundial move backward as a sign for King Hezekiah.
The Bible gives two versions of the story of King Hezekiah and the sundial. First in 2 Kings, Chapter 20.
8 And Hezekiah said unto Isaiah, What [shall be] the sign that the LORD will heal me, and that I shall go up into the house of the LORD the third day? 9 And Isaiah said, This sign shalt thou have of the LORD, that the LORD will do the thing that he hath spoken: shall the shadow go forward ten degrees, or go back ten degrees? 10 And Hezekiah answered, It is a light thing for the shadow to go down ten degrees: nay, but let the shadow return backward ten degrees. 11 And Isaiah the prophet cried unto the LORD: and he brought the shadow ten degrees backward, by which it had gone down in the dial of Ahaz. (2 Kings 20: 8–11, King James Version)