I'm sometimes puzzled with why I can do things in a notebook, save and quit, reopen it, and get errors upon recalculating cells. Simple example... This worked once. At least, I don't /think/ I changed anything:
Convert[SpeedOfLight, Inch / Second]
It complains that there are "Incompatible units." I'm sure this is really simple, but I really can't figure out what changed.
Any help appreciated, Joel