Rashi on Isaiah
Behold I return the shade backwards ten steps which it went down.
Rashi on Isaiah
the shade of the steps A sort of steps made opposite the sun to determine the hours of the day, like the clocks (horloge in French) that craftsmen make (sectarians make [Parshandatha]).
Rashi on Isaiah
that it went down It hastened to go down, and the day was shortened by ten hours on the day Ahaz died, in order that they should not eulogize him, and now they went backwards on the day Hezekiah recovered, and ten hours were added to the day.