olbrich/ruby-units — pull request #61 by stwr667 (2013-01-25 09:11:21+00:00)
Title: Fix failing case of subtraction losing Units class

Currently if you subtract 2 Units that are zero, the result is not a Unit, but the scalar object. However if you add them, it respects the Units class correctly.

Here is the fix and 2 tests that prove it.