Machine M fills packets with mean weight 500 g and standard deviation 20 g. Machine N fills packets with mean weight 250 g and standard deviation 15 g. Which machine is more consistent?

Consistency is judged by the coefficient of variation, CV = (standard deviation ÷ mean) × 100. Machine M: (20 ÷ 500) × 100 = 4 percent. Machine N: (15 ÷ 250) × 100 = 6 percent. The smaller CV wins, so M is more consistent even though its standard deviation is the larger one — spread has to be measured against the size of the values being measured. Also 20/500 = 0.04 while 15/250 = 0.06, so the two ratios are not equal.