A sundial to tell the time

One highly interesting detail is the splendid sundial that spans forty metres along the transept between the chapels of St. Benedict and St. Nicholas of Bari.
The extraordinarily precise measuring instrument was created between 1839 and 1841 by two astronomers, W. S. von Waltershausen and C. Peters of Denmark. It uses the light that passes through the gnomon, the hole on the vault of the transept located 23 metres, 91 centimetres and 7 millimetres high, to mark the hours, days, months and zodiac signs.