C Chart

In this chart, we plot the number of defectives (per batch, per day, per machine, per 100 feet of pipe, etc.). This chart assumes that defects of the quality attribute are rare, and the control limits in this chart are computed based on the Poisson distribution (distribution of rare events).

The C chart is described in most standard quality control textbooks; see for example, Hart and Hart (1989), Juran (1962), Juran and Gryna (1970), Montgomery (1985, 1991), or Vaughn (1974).