Heures de Charles d'Angoulême
Diagram for calculating the date of Easter
On the reverse of the Ave Maria is a diagram for calculating the date of Easter. Originally, "the vivid colours of the concentric circles behind the diagram must have stood out more clearly against the cream-coloured parchment [however] one of the components used to make the golden ground of the Ave Maria, probably silver, has gone rusty and seeped deep into the parchment". The main spoke, pointing up, features a sequence of nineteen Roman numerals representing years in the Metonic cycle.