'Sundial' in the Bible

So Isaiah the prophet called out to the Lord, and He brought the shadow on the steps ten steps backward by which it had gone down on the sundial of Ahaz.

Listen carefully, I will turn the shadow on the stairway [denoting the time of day] ten steps backward, the shadow on the stairway (sundial) of Ahaz.” And the sunlight went ten steps backward on the stairway where it had [previously] gone down.