Ah, great! Perhaps you could start a thread that explains your conversion. I know I'd be very interested.
Anyway, for a DOD chart, I would use this (
found here).
So, if you're measuring a 48V system, 42V would be your absolute minimum you'd ever want to go. 50% dod would be down to 48.2V.
If you are using unbalanced batteries, you really want a meter like the link I posted before that monitors each battery. However, if your batteries are pretty well matched, you can just use a regular voltmeter.