I think that scale and precision are rights.

Take a look at concept used in rails or databases for example:
http://millarian.com/programming/ruby-on-rails/precision-and-scale-for-ruby-on-rails-migrations/
http://msdn.microsoft.com/en-us/library/ms190476.aspx
http://stackoverflow.com/questions/5689369/what-is-the-difference-between-precision-and-scale-in-oracle