Precision Laboratories QAC test papers and strips utilize an effect commonly referred to as the “protein-error of indicators” to quantify the QAC ppm levels. While first observed with proteins (thus the name), the technique utilizes pH indicators and buffering systems to create an environment where the test paper or strip reacts (develops color) proportional to the amount of analyte (QAC) present. The PL QAC test papers and strips have color charts calibrated to solutions prepared from OASIS 146, an industry standard QAC product. The performance of the papers and strips with alternate QAC products should always be verified. In addition, any additives should be evaluated to see if they contribute to the “protein-error” effect.