Alcotest Tolerance Calculations: DWI Case Law

January 28, 2010

In another episode of “Cases you should not Appeal”, the Appellate Division, in State v. Rivera ruled that it is improper to truncate calculations to three decimal places when applying the Chun Tolerance Calculation Worksheet to determine of Alcotest reading are within accepted tolerances. In every Alcotest DWI trial and prosecution, the state must show that the readings from the two valid breath test were within tolerance.

Tolerance refers to an upper and lower limit that the DWI suspect’s Alcotest results must fall within. This is a mathematical equation set forth in State v Chun. After the calculation is performed, and it is determined that the readings are out of tolerance, than the readings are inadmissible. This happens from time to time. Usually, the police or testing trooper will perform the calculations on the spot to determined the validity,and to guard against future challenges. In many cases, the calculation performed will only be calculated to the third decimal. The Chun decision and Order states that it should be calculated to the fourth.

After performing hundreds of these calculations myself, It became apparant that the three decimal method was more beneficial to the defendant. Using three decimals instead of four yielded more out of tolerance readings,  and the occasional suppression of the Alcotest results.

In State v Rivera, the defendant argued, among other things, that the reduction to three decimal places is consistent with Chun’s adoption of truncating the lowest score to benefit defendants charged with per se violations of the DWI statute. However, the defendant could not point to any language in the case that would support that claim. Additionally, the Chun Court did specifically proscribe the 4 decimal point standard in the decision.

The effect of this decision will likely be that all municipal prosecutors will make sure that the calculations were done to the fourth decimal when presented with an out of tolerance reading, closing the loop just a little tighter. In my opinion, the argument was probably doomed from the start, but it was an argument nonetheless. The question that you have to ask yourself though is do you want to appeal a case that has very little chance of succeeding, and will created bad case law for defense attorneys and DWI defendants. In theory, the defendant was asking the Court to make DWI laws more lenient. In New Jersey, this is not a popular request. If you are going to ask, you better have some serious ammunition, and I don’t think they had it here.