Known as Queen Mary’s Dial, this is the finest example known of the facet head class.  It is formed from a sandstone icosahedron 18 inches high, standing on one of its corners. The 20 triangular facets are elaborately carved with coats of arms and monograms of King Charles I and his Queen Henrietta Maria.  Various bowl, heart-shaped and triangular sunken dials are incorporated.  In some of these the nose of a carved face acts as a gnomon, while other gnomons are of open fret worked metal.  The top of the pedestal is an inverted hemisphere, which stands on a square column, decorated with acanthus leaves, and mounted on three high spreading octagonal steps (probably later than the dial).

The dial was designed for the Scottish Coronation of Charles I and is dated 1633.   It was made by John Mylne III, Master Mason to the king.  Royal Accounts show that it cost £408 15s 6d (Scots) plus further charges for painting and gilding, this additional charge illustrating that at the time it was customary to paint these stone sculptures.  It was restored in Queen Victoria’s time, and when recorded by Andrew Somerville in 1986, it had been cleaned recently.