Alcohol Breath Testing and Least Squares Data Fitting

The above link is to a study at North Carolina State University investigating the mathematics behind how breathalyser tests calculate a persons Blood Alcohol Content (BAC). It turns out (not surprisingly) that if a person takes several breathalyser tests one after another, their results can vary quite a bit. The variations are caused by any number of environmental factors and the length of time the individual exhales for. The BAC recorded will increase initially for the first few seconds of exhaling, eventually dropping and leveling off at some value. Some testing devices will simply use the highest BAC recorded as the return value, even though it may represent an inaccurate result. The study found that by using a least squares fit to find an estimate that closely follows the data points will result in a much more accurate reading of BAC.