Excel Spreadsheet Templates for Quality Control, Control chart for percent defective. In all of the control charts, the basic idea is to sample from a continuous production process at equal intervals of time and record some quality characteristic. Common quality characteristics include the percent defective (P-CHART). If the process is under control, the quality characteristics should vary about the population mean in a random manner. If a sample mean falls outside the control limits, there is a very small probability that this happened due to randomness or chance alone and the process should be investigated
