I have not yet run across anything that explains diacritical marks in medieval through enlightenment Latin texts. I am using a volume of Le Clerc's Logica, from 1692 and often reprinted through the early 1700s, that can be found on Google Books (books.google.com) with the identifier (/books?id=YK2Zu3gsEmQC). There you will find words with a accent grave, such as: verò, à, cùm, propriè, quòd, verùm, vulgò, minùs, quàm, secundò, quò, merè, tertiò, imò, and aequè. You will also find words with a circumflex, such as these: figurâ, motûs, certâ, dictâ, auditâ, hîc, and usûs. Any explanation--or pointers to an explanation--of the use of these grave and circumflex accents would be appreciated.