Grimorium Verum (Latin for "The True Grimoire"), supposedly written in 1517 Memphis, Egypt, is a spellbook of magic, going in-depth of some ritual practices and spells. The book is divided into four chapters (books):
1 - Demonology, going in detail about the characters of the Demons, their names, powers, and sigils.
2 - Natural and Supernatural Secrets, which speaks of planetary hours and conjuration.
3 - The Key, which explains the requisites and preparations for those, wishing to do the work described in this book.
4 - The Holy Kingdom, which provides spells and ways to conjure Demons and Inferior Spirits.
It is well put together and providing great detail in regard to the subjects it explores. Like most Grimoires, Grimorium Verum claims a tradition originating with King Solomon and draws upon Hygromanteia (Magical Treatise of Solomon).
Sadly, there is no evidence that this work is older than the 18th century, making references to books published way beyond the original date provided. Nonetheless, it is still an interesting piece of Magical history and there is definitely value within it.