Why is 0.01 often used for zero tolerance testing?

With a breath test instrument, as long as the sampling was preceded by a 15 minute deprivation period, results of 0.01 or above, on a properly calibrated instrument, indicates that alcohol is present. This is consistent with the reporting of blood samples.  Blood samples are usually reported as a two digit result (.##) therefore, when using blood, 0.01 is the lowest reported result.