I have commented repeatedly in the past about the inaccuracy and
unreliability of breath-testing devices used in DUI
investigations. This is due to a wide range of factors: inherent
design defects (see, for example, my previous post "Why
Breathalyzers Don’t Measure Alcohol"); ineffective calibration
and maintenance of the machines; improper administration of the
test; radio frequncy interference; and, most importantly,
physiological variability in humans. The main problem with
breath machines is that they are designed to assume all human
beings are the same (see "Convicting the ‘Average’ DUI
Suspect"). In fact, we are all very different from one another
in ways that are critical to such testing — and we are ourselves
physiologically different from one moment to the next. Each of
us, for example, is inherently different in our partition ratio
— the ratio of alcohol in our breath compared to alcohol in our
blood — and this ratio differs within ourselves from hour to
hour (see "Breathalyzers — and Why They Don’t