It's more of an intro level book, aimed at scientists rather than numerics geeks or or people into theoretical math. So it does a good job of presenting things simply and in ways that don't require navigating too many fine points. That approach mostly works, though it leaves openings for things to go wrong. The topics (root finding, integration, etc.) are similar to what you'd see in an undergrad numerics course. It specifically doesn't have anything about PDE's, since it defines that as the boundary between introductory and advanced topics.