In medieval times, time was kept by means of sundials, water-clocks, hourglasses or (from the thirteenth century onwards) various mechanical devices (some of which struck the hour). The word oriloge seems to have been used for all of the above, although in most Anglo-Norman attestations the specific nature of the mechanism is not stated.

The two attestations of the word translated as ‘sundial’ both refer to Isaiah 38.1-8, a passage which describes how the prophet Isaiah causes the shadow on the sundial of Ahaz to move backwards ten degrees as sign of God’s power in order to make Hezekiah, king of Judah, repent.