isaiah 38:8 Behold, I will bring again the shadow of the degrees, which is gone down in the sun dial of Ahaz, ten degrees backward. So the sun returned ten degrees, by which degrees it was gone down. - Free Bible Online

      8. bring again--cause to return (Jos 10:12-14). In 2Ki 20:9, 11, the choice is stated to have been given to Hezekiah, whether the shadow should go forward, or go back, ten degrees. Hezekiah replied, "It is a light thing (a less decisive miracle) for the shadow to go down (its usual direction) ten degrees: nay, but let it return backward ten degrees"; so Isaiah cried to Jehovah that it should be so, and it was so (compare Jos 10:12, 14).
      sundial of Ahaz--HERODOTUS (2.109) states that the sundial and the division of the day into twelve hours, were invented by the Babylonians; from them Ahaz borrowed the invention. He was one, from his connection with Tiglath-pileser, likely to have done so (2Ki 16:7, 10). "Shadow of the degrees" means the shadow made on the degrees. JOSEPHUS thinks these degrees were steps ascending to the palace of Ahaz; the time of day was indicated by the number of steps reached by the shadow. But probably a sundial, strictly so called, is meant; it was of such a size, and so placed, that Hezekiah, when convalescent, could witness the miracle from his chamber. Compare Isa 38:21, 22 with 2Ki 20:9, where translate, shall this shadow go forward, &c.; the dial was no doubt in sight, probably "in the middle court" (2Ki 20:4), the point where Isaiah turned back to announce God's gracious answers to Hezekiah. Hence this particular sign was given. The retrogression of the shadow may have been effected by refraction; a cloud denser than the air interposing between the gnomon and dial would cause the phenomenon, which does not take from the miracle, for God gave him the choice whether the shadow should go forward or back, and regulated the time and place. BOSANQUET makes the fourteenth year of Hezekiah to be 689 B.C., the known year of a solar eclipse, to which he ascribes the recession of the shadow. At all events, there is no need for supposing any revolution of the relative positions of the sun and earth, but merely an effect produced on the shadow (2Ki 20:9-11); that effect was only local, and designed for the satisfaction of Hezekiah, for the Babylonian astronomers and king "sent to enquire of the wonder that was done in the land" (2Ch 32:31), implying that it had not extended to their country. No mention of any instrument for marking time occurs before this dial of Ahaz, 700 B.C. The first mention of the "hour" is made by Daniel at Babylon (Da 3:6).

JFB.