The accuracy of such clocks was better than 1 s per day, and the observations of stellar transits allowed their synchronization with sidereal time.

The names of some bright stars are engraved on the meridian marbles in the positions that they had in 1702. Sirius, the brightest star, is near the number 161.

Fig 1 Sun transits at the same altitude of Sirius as in 1702 ( Feb. 4, 2005 )

Bianchini reported the observations of Sirius at noon in June-July 1703. The windows of the Basilica were darkened with external tents and, at the same time when the pinhole solar image was crossing the floor like nowadays, the star was observed from the telescope. The prolongation of the line of sight of the telescope on the Line corresponded to the altitude of the star at the meridian transit. Other stars have their name and right ascension engraved on the marbles, being the meridian altitude indicated by the position of the brass star.

Fig 2 The telescope used in the observations of stars on the Clementine Line