Floating point types have a reputation for being difficult to use compared to integer types. This is partly because they have unintuitive sources of rounding error but it also stems from the kinds of calculations they are used for, which contain plentiful other sources of numeric error.
The float_eq crate provides an API for comparing floating point primitives, structs and collections for equality that allows users to communicate their reasoning and intent with respect to numeric error.
This book is not designed to be read from cover to cover, but instead is a series of categorised articles. If you are unsure of how floats work or why they are considered difficult to use then begin with the Basic Usage guide, otherwise check out one of the categories for more: