The purpose of the instrument was to standardise the measurement of time and the calendar. The convention in Sicily had been that the (24-hour) day was measured from the moment of sun-rise, which of course meant that no two locations had the same time and, more importantly, did not have the same time as in St. Peter's Basilica in Rome. It was also important to know when the Vernal equinox occurred, to provide the correct date for Easter. On the belltowers there were six medieval bells.