The surviving copies of the Aberdeen Breviary contain many differences. Bringing them together to examine these differences can further our understanding of the printing process in the early 16th century.
Here is one example:
Our original set of the Aberdeen Breviary contains an error where the heading for the feast day of St Julian is printed in black.
In the Glamis Castle copy, this is printed in red and set out more clearly, showing that the printers made corrections as they went along.