The criteria of precision, SD and CV were calculated from the different data. Because the units of max. y1 and y2 values were differed, we could not compare their precision with this standard deviation value. The coefficient of variation CV is a numeric value without a unit. This index could be used to assess precision. The CV values for three different indexes treated with or without vegetable juice are presented in Fig. 3. From the data distribution of the three indexes, l max y1 and y2 (Fig. 3), the y2 index had the lowest CV values and the max index had the highest CV values for five concentra- tions. The results of the comparison of CV values indicated the y2 values had the best precision.