The Book of Tempus is an extremely old book written in Latin as well as several versions of Ancient Greek. The exact age of the book is unknown as it is well-preserved, even the natural occurrence of mold forming within the pages not having transpired. The book contains pages and pages that apparently teach the reader how to make items capable of manipulating time.
The book itself appears to contain no powers of its own, but within its pages are extremely long and detailed rituals that can teach a person who to make an item capable of manipulating time. Various examples are detailed within, including a paintbrush, a lyre, a staff/cane, a sundial, a mirror and an hourglass. The Tempus Clock was one such item made from the book, requiring months of work to make possible. Some spells for the Wand of Kronos were also detailed, including how to use it to travel through time.