Figure presents the variation in a single data point extracted from Ref. Figure : Variation in the value of single data point extracted 9 times, 3 times per each data digitization software: web plot digitizer (green), plot digitizer (orange) and graph reader (blue). The mean of each software extraction is used as a reference value while the mean absolute percentage error is used to quantify the data uncertainty. Data extracted from reference . times using the three programs. The mean value of the three points is assumed to be the "true" reference value and the Mean Absolute Percentage Error (MAD), calculated as