convertable_values

https://github.com/stephenb/convertable_values

Convertable Values provides a simple unit conversion library and pattern for transparently storing base units. Example usage: You have a model that wants to store values with units (e.g., 200 lbs), but you want (or at least should want) to store all the values in a base unit (e.g., 90.718474 kilograms). This gem makes using this design pattern totally transparent.