DUI Metrology Dictionary
"Over time" an electronic signal can, and probably will, drift due to dust, dirt, and deterioration of electronic components. Intoxilyzers inevitably get exposed to all sorts of foreign objects and phenomena including cleaning fluids, vomit, spit, and interferents. Unfortunately there is very little or no research on this phenomenon in police-controlled settings. New Intoxilyzers cannot be bought. The CFS and other state labs are not sampling old instruments in the field and writing scientific papers about their findings. Governments resist FOI applications respecting the deterioration of their instruments over time. VIM 4.21(5.16) defines instrumental drift as "continuous or incremental change over time in ndication, due to changes in metrological properties of a measuring instrument. NOTE Instrumental drift is related neither to a change in a quantity being measured nor to a change of any recognized influence quantity."