I think all this talk has convinced me to get a blood meter for fun of it and replace my Ketonix - it's had a good run but the variability of the measurements depending on time of day, amount of exogenous fat consumed, my mood, testing method (blowing into a tube for x time is not very easy to quantify) etc, etc.

Anyone want a Ketonix (first edition - powered USB) I'll send it if you pay shipping

Thanks again Teaser for your insights and research.