My main motivation for creating this package was dealing with physical quantities. As a developer you adhere to a specific set of units that are used throughout your application, but for a user it might be just convenient to specify these values in different units. Say your program uses the SI unit system for its internal calculations and therefore you declare the length of some object in units of meter. But your users might specify objects of various magnitudes and therefore, for the sake of convenience, use different units such as centimeter or millimeter. Having a mechanism that automatically converts the specified values such that they meet the declaration is one of the many features of this package.