Calculate the upper control limit (UCL) and low control limit (LCL).Compute p̅ = total number of defectives / total number of samples =Σnp/Σn.Calculate each subgroup non-conformities rate= np/n.The subgroup size must be large enough for the p chart otherwise, control limits may not be accurate when estimated from the data. Where np = number of defectives in the sample.The testing procedure should be the same for each lot.There should be two events (pass or fail), and they are mutually exclusive.The probability of non-conformance is the same for each item.Similarly, the p chart plots the proportion of defective items.

np chart is for the number of defectives, and u chart is for the number of defects per unit, c chart is for the number of defects. There are basically four types of control charts that exist for attribute data. p charts are used when the subgroups are not equal in size and compute control limits based on the binomial distribution. P chart is one of the quality control charts used to assess trends and patterns in counts of binary events (e.g., pass, fail) over time. Unlike variable charts, only one chart is plotted for attributes. For example, the number of tubes failed on a shop floor. X̅ and R charts are used for measurable quantities such as length, weight, and height. Attribute control charts are used for attribute data. In other words, the data that counts the number of defective items or the number of defects per unit. Selection of an appropriate control chart is very important in control charts mapping, otherwise ended up with inaccurate control limits for the data. The control limits are ☓σ from the centerline. A control chart always has a central line for the average, an upper line for the upper control limit, and a lower line for the lower control limit. The control chart is a graph used to study how a process changes over time. The centerline of the p chart (p̅) is the total number of Defectives or non-conforming units divided by the total number of items sampled. In the p-chart, proportions are plotted on the y-axis, and the number of samples is on the x-axis. It uses a Binomial Distribution to measure the proportion of defective or non-conforming units in a sample. It is used to analyze the proportions of non-conforming or defective items in a process. Attribute charts: p chart is also known as the control chart for proportions.

2 sigma control chart