Books as Instruments

Regiomontanus,  Calendarium (1476), volvelle

In this remarkable book, Regiomontanus predicted the positions of the Sun and Moon for 40 years. He designed a sundial to work independently of one︎'s latitude, and a volvelle, or circular dial, to locate the position and phase of the Moon according to date and time. Books became observing instruments in their own right.