ABSTRACT
This chapter presents control charts and demonstrates attainment of statistical control of a mass calibration process. An appropriate check standard weight is weighed at established intervals and the measurement results are plotted on a chart. The measured values are represented on the ordinate Y-axis and the sequence of the measurements is represented on the abscissa X-axis. A horizontal line is drawn representing the mean of the measured values. The mass calibration system is considered to be in statistical control if subsequent measurements fall within the control limits. The use of control charts can also detect long-term drift in a measurement process. The statistical information on which the control limits are based can be used to calculate confidence uncertainty limits for measurements made while the measurement system is demonstrated to be in statistical control. Control charts utilizing mass reference standards at two or three load ranges, appropriately spaced within the range of the test, are satisfactory.
