[Reliability of back-calculation of blood alcohol concentration to the time of infraction].

In order to be able to give an accurate legal judgement of a drink driving offense, the BAC at the time of the offense has to be determined. The calculation which may be necessary is based on the time of blood sampling and on the time of the offense. The authors examined records of 854 blood samples taken in the years 1979 and 1989 with regards to the times recorded. Blood sampling recorded on the hour or on the half hour could be found four times more frequently than would have been statistically expected. Blood sampling recorded to the nearest five or ten minutes were documented three times as often as those ending on the exact minute. Times of the offense were recorded at least ten times as often to the nearest five minutes. The rounding up of times could cause discrepancies of more than 0.01% when calculating the BAC at the time of offense.