Which two control charts should be used in combination when monitoring a process using varlable measures? a. P-chart and C-chart b. L-chart and K-chart c. Z-chart and Q-chart d. X-bar chart and R-chart Process capability is an important measurement that compares a, the design specifications to the natural process variation. b. the proportion of acceptable quality to the statistically expected percentage. c. random variation to non-random variation. d. the number of defects to the number of good products