Crowley adapted Liber Samekh from the Greek Magical Papyri's V.96—172,  in which Akephalos (The Headless One) is invoked. The PGM passage is  known as the The Stele of Ieu.  It is used by modern Hermetic Arts Practitioners as a means to contact  one's Holy Guardian Angel, and there are a plethora of modern experience  reports from those who have performed it.