A calibration log is a record of accuracy checks and calibrations performed on a specific breath alcohol testing instrument. A calibration log is a record-keeping requirement of the U.S. Department of Transportation alcohol testing program and must be retained for at least 2 years or as long as your instrument is in service.  Information recorded in the log must include the date and time of the procedure, who performed it, where it was performed, the lot number of the gas standard used, the expected/target value and the result. The logbook is necessary to prove the accuracy of your testing device at the time of a particular test as well as to show the stability and accuracy of your instrument over time.