Pi is actually about 3, an accurate statement to one place of precision. For the purpose of that conversation, describing the bookshelf to the nearest foot is precise enough. It is useful to work to the nearest foot when working on the initial design of a house. In cutting the lumber, it is necessary to be accurate to greater precision, perhaps the nearest inch, half-inch, or eighth of an inch. We speak of accuracy with respect to the precision needed at the time.
Scale is a matter of hiding things in order to cover more material.
To show a map of the city, we might omit everything less than 100 feet long. The six-foot bookshelf does not show up at all. When you choose a scale at which to operate, it dictates the amount of precision that you can use. Scale and precision are related. On a software development project, these terms have analogous meanings and uses.