another great way to keep units straight is to use a freeware program called SMath Studio. The have a live version on their webpage (
http://en.smath.info/) and try it out. I use it for FRC calcs as well as in my professional life to document calculations for clients. It's a wonderful tool and functions much like MathCAD.
as a note, units can be inserted with the ' (apostrophe) key.
You can also download a portable version here:
http://smath.info/wiki/(S(iymz0v3hva...with%20Plugins