One of the fancier methods the prosecution and the law uses to determine your blood levels at the time you were driving is retrograde extrapolation. This is a mathematical calculation of what your blood alcohol levels must have been when you were driving, given its current levels. This type of calculation is often made when blood alcohol levels, at the time of testing, are lower that expected. It is used to suggest that your levels must have been higher when you were driving. Because everyone's metabolism is different and because the amount of food in your system can change the rate of absorption, retrograde extrapolation is very suspect. It is important to challenge such suppositions. The information contained in this message is general and should not substitute for the advice and counsel of a licensed attorney.