GNOMON

No, I didn't know what it meant either..... It's a meridian line or the part of a sundial that casts a shadow. It was traced on the floor inside the Hôtel Dieu in Tonnerre. When the rays of the sun come through a tiny hole in the wall, it is noon in Tonnerre.

Hole the sun shines through

Part of the Gnomon in the Hôtel Dieu

The sun shines in a beam onto the floor and illuminates the time, day and month. The area and length was much larger for the winter months as the sun is much lower. This was constructed in the 18th century by a Benedictine monk. Unfortunately the day we were there it was cloudy so we had to use our imagination!!