Finally! Out of confusion comes clarity: http://www.betabase.info/ Measuring from DPO makes so much more sense (and is WAY more accurate) than LMP.
It doesn't matter. Just pretend your LMP was 14 days before you ovulated. I had a long cycle and know I ovulated at day 24, but I'm not going to spend the next 8 months telling people how by LMP my due day is July 24, but by O it's August 4... I just moved my dates to what physically is true.