APA (7th ed.) Citation

Gregory‏ XIII,‏ Pope, 1. (1583). Calendarium Gregorianum perpetuum. Ex officina Christophori Plantini.

Chicago Style (17th ed.) Citation

Gregory‏ XIII,‏ Pope, 1502-1585‏. Calendarium Gregorianum Perpetuum. Antverpiae: Ex officina Christophori Plantini, 1583.

MLA (9th ed.) Citation

Gregory‏ XIII,‏ Pope, 1502-1585‏. Calendarium Gregorianum Perpetuum. Ex officina Christophori Plantini, 1583.

Warning: These citations may not always be 100% accurate.