That's OK - I get "Senior's Moments' as well. ~(;-))

Cadency markings are a specialised area of the general subject of Heraldry and, as such, is far too complicated to try and give an explanation here. Have a look at http://en.wikipedia.org/wiki/Cadency and, in addition to the bibliography given there, I would add "Boutell's Heraldry" as revised and edited by the late J. P. Brooke-Little, one time Clarenceux King Of Arms at the College of Arms in London. This book is the easiest volume on the subject of Heraldry to read/understand in the English Language. The latest edition of this work was produced in 1983.

In addition, I could recommend also reading "Heraldic Cadency", a book by Gayre of Gayre and Nigg (1961)