you're right, flatland - the scangauge doesn't measure actual flow, it's a calculation based on pulse width, air flow, displacement and other factors. that said, it's been pretty darn accurate for me (within 2% of "manual" calculations on the gas receipt at fill-up time).
FYI... been watching eBay for about 3 weeks now for a used laptop-connectable OBD2 unit for proper data-logging ability.
kicked myself on friday because i missed out on a real deal: it went for $50 - and the only reason i missed it is because of a web/browser glitch at the crucial bidding moment (15 sec before the auction ended).
i don't really want 2 separate units. the scangauge is so convenient since it's self-contained, no muss, no fuss. i think i posted this elsewhere here, but i did write to the company to see if they would ever consider adding a USB/serial output, and they basically said no.
how hard would it be to add one? opinions of any electronics experts??