What's wrong with breathalayzers?

Dr. Dubowski testified that his research determined that in only 2.3 percent of the tests did the breath reading overstate the actual BAC. This was the first time this number was made publicly available; it had not been presented in his 1985 report.
Another witness in the Downie case, Dr. Gerald Simpson, a physical chemist also testified, and attempted to describe the variables that could render a Breathalyzer reading inaccurate. The court largely disregarded his testimony in favor of the assured endorsement of breath analysis offered by Dr. Dubowski.
The court determined that the use of breath alcohol was scientifically valid for the purpose of determining BAC. Was that the end of the story? Not quite.
After the Downie trial, Dr. Simpson obtained the actual data from Dr. Dubowski’s 1985 report. In applying the same analysis to the data that Dr. Dubowski used, Dr. Simpson discovered a major error. The incidences when breath analysis overstated actual BAC were not 2.3 percent of the tests, as Dr. Dubowski had testified to in the Downie case, but rather 23 percent of the tests – a wandering decimal point!
Another fantastic resource concerning breathalyzers is the DUI blog listed below.
Links: http://www.motorists.org/blog/its-just-a-decimal-point-the-dirty-secret-behind-breathalyzers/
http://www.duiblog.com/