We need to work out a plan for built-in use of units. Rough sketch of the benefits:

• Automatic appropriate labels for plots
• Better sanity checking on calculations

There exists the quantities package that provides a great numpy subclass that provides unit-handling. Unfortunately, this does not work with masked arrays, which are a separate numpy subclass. Also, I'm not sure we want to rely on this as an external dependency.

I lean towards making an internal fork of quantities that gives us masked values, unit support, as well as support for arbitrary metadata.