La meridiana di Egnazio Danti nella Torre dei Venti in Vaticano:   un'icona della riforma Gregoriana del calendario
  The meridian line traced by Egnazio Danti in the Torre dei Venti in Vatican demostrated the need of the Gregorian Reformation of the Calendar. A review on this instrument is presented, along with the astrometric recognition. This meridian line, dated 1580, is deviated of 72 arcminutes Westward from the true North. 
Costantino Sigismondi
physics.hist-ph astro-ph.IM