This is a special type of sundial called a 'polyhedral dial' because it is made in a complicated shape. It can be used to tell the time in a number of different ways from the position of the sun. It is a very precious object and is completely covered in gold. Made for Cardinal Wolsey (bearing his arms, the arms of York Minster and two representations of a cardinal’s hat), by Nicholaus Kratzer, this was a typical conjunction of astronomical and cosmographical interests. Born in Munich and educated at the universities of Cologne and Wittenberg, Kratzer was an instrument-maker, who brought the craft practice of astronomy to England in about 1517, arriving, according to a contemporary account, bearing astrolabes and armillary spheres.
In the Renaissance, 'polyhedral' dials like this one were less useful as things to be used everyday and more like things that had all the up-to-date technology and theories built into them. They were made so that mathematicians and instrument makers could show off their skills and demonstrate that they had mastered all the new mathematical theories and techniques in something that actually worked.
Like all sundials, this one works by casting the shadow of a spike called a 'gnomon' onto a series of lines that have been calibrated to show the time. In a polyhedral dial the challenge was to build as many different individual sundials onto as many different faces as possible. This sundial has nine different faces, which is good going. If it is made correctly then all the dials on all the different faces should show exactly the same time no matter what direction the sundial is pointing in.