Idiom meaning, usage examples, facts

1. The pilot might have carried out some preflight procedures more quickly, but because he was training a new pilot, he did everything by the book so the trainee would learn the procedures.
2. As a parent raising children, you can’t always go by the book and follow the rules. Sometimes you have to use your intuition.

The expression probably originates from the idea that the procedure or accepted rules of an established game are set down in a book.