Xbar R Chart versus Xbar S Chart I recently got a question from a reader that wanted to know when to use an Xbar R chart versus Xbar S chart. In this post, I will answer that question. Well, the decision to use either of these Statistical Process Control Charts comes down to how the […]

## Xbar and R Chart Formula and Constants Deriving Control Chart Constants: d2, d3, A2, D3, D4 and Computing Control Limits

Have you ever had to prepare an Xbar and R chart? If so, you most likely used some type of software package to display your data and compute the necessary control limits for your Xbar and R chart. But, have you ever wondered how these control limits for an Xbar and R chart were computed? […]

## Control Chart Constants – How to Derive A2 and E2 Learn how to derive the E2 and A2 control chart constants used to compute control limits for the X-bar and Individuals Charts

Control Chart Constants, where did the A2 and E2 constants come from? In statistical process control (SPC) charting, we use the A2 and E2 constants to calculate control limits for an Average (X-bar chart) and Individuals charts. But where do the A2 and E2 constants come from? Let’s look at the following example, for an X-bar […]

## D2 values for the Distribution of the Average Range Continuing Series in Range Statistics

D2 values for the distribution of the average range appear in the following table. The columns and rows represent the subgroup size (n) and number of subgroups (k). For a given subgroup size, say n=2, notice that the value of d2 changes as the number of subgroups, k, increases. As an example, notice that d2=1.150 […]

## D2 Values Used in Gage Repeatability and Reproducibility Studies Continuing series on Gage R&R Studies

D2 values appear in Gage RR equations when using the Average and Range method. The Average and Range method uses constants to estimate Gage Repeatability and Reproducibility (GR&R). There are two “K” constants “K1” and “K2”. Quality Engineers use them to estimate repeatability and reproducibility. Each of these “K” constants use d2 values in their […]