This may seem like a silly recommendation, as it is a minimum standard to know the National Electrical Code. But this recommendation is more specific to the Handbook edition of the NFPA 70. This is a more expensive version of the book that has images, notes, and extra text that go deeper into the code and help to explain the “intent” of the code within the code itself. This is just an interpretation of the code, just like anyone else’s, however it is written by the NFPA – the people who write the NEC. It’s a little steep in cost, but worth having a copy of for the extra explanations for sure.