The Principia Mechanicum is a text that lays down the many traditional guidelines on the working of the machines to the disciples of the Adeptus Mechanicus.
Within it, the tenets by which all machines were governed were documented within the prescriptive doctrines of this text. After passing the basic competancies of the Principia, students were inducted formally into the Cult Mechanicus and were branded with electoos on the back of their hands. Before the start of the Horus Heresy, Dalia Cythera had been using the Principia Mechanicum hidebound traditions during the construction of the Sigma-Phi Desolator Engine.1
- 1: Mechanicum (pg 96)