Pursuant to RCW 46.61.506 the following method is approved for determining whether two breath samples agree to within plus or minus ten percent of their mean.

(1) The breath test results will be reported, truncated to three decimal places.

(2) For the DataMaster instruments, the mean of the two breath test results will be calculated and rounded to four decimal places. For the Drager instrument, the mean of all four results will be calculated and rounded to four decimal places.

(3) The lower acceptable limit will be determined by multiplying the above mean by 0.9, and truncating to three decimal places.

(4) The upper acceptable limit will be determined by multiplying the mean by 1.1 and truncating to three decimal places.

(5) If the individual results fall within and inclusive of the upper and lower acceptable limits, the two breath samples are valid.