https://books.google.com/books?id=YoIzY0PdSjIC&pg=PA57&lpg=PA57&dq=mapping+calendar+to+clock&source=bl&ots=5uMX8NAa9B&sig=ACfU3U2qk1dVDR3BL8F_OoVe9CY647jzzw&hl=en&sa=X&ved=2ahUKEwjlkeWDhO7oAhWDZDUKHXqlCLcQ6AEwGnoECBQQLQ#v=onepage&q=mapping%20calendar%20to%20clock&f=false
https://www.amazon.co.uk/Calendar-5000-year-Struggle-Heavens-Happened/dp/1857029798