Since parsing units from a string can be tricky, I have gone through all of
the networks available via the fdsnstation web service and pulled the units
out. Luckily, there are only 41 distinct strings as unit names. To aid in
converting values, I have put together a csv file with three columns:
1) unit name from the xml
2) my best guess at how to "SI" the unit (some are, um, nonstandard)
3) a "description"
The only case I found of a unit name meaning two things in two different
channels was the symbol M which means "meter" in most places, but "minute"
in a small number of channel responses.