You could get a toxicologist to testify, but he or she will have to start with the blood alcohol level that was established by the certificate, if there was no problem with the device, in other words if there were no errors. He or she will have to start with the fact that you were at 0.12 when you were tested at, say, 10 o'clock, and calculate that you would have been at 0.07 when you left the bar, based on how much you drank.
On June 19th, 2007. See this statement in context.