Fig. 4

Individual moving range control charts for toluene yields (μg/puff) from the highest gas concentration (99.5 ppm). a Top, individual measurements for all data points (n = 120). Bottom, difference between two consecutive data points (moving range). b Variability in repeats per analytical run (n = 10). The charts in a were broken down into 12 sections with their own upper and lower control limits as indicated by the dotted lines. Top, individual measurements; bottom, difference between two consecutive data points