Author: SIGMADESK

Process capability indices, Cp and Cpk, are two of the most commonly reported numbers in quality engineering. They’re calculated from the same underlying measurement data but they answer two different questions, and confusing them can lead to the wrong conclusion about whether a process is actually capable. This article focuses specifically on the distinction between […]

A practical guide to standard deviation — what it measures, why it matters, and the difference between population and sample standard deviation explained with clear examples. Standard deviation is one of the most important concepts in statistics. It appears in manufacturing quality control, finance, healthcare, scientific research, and virtually any field where data needs to […]

A practical guide to control charts — from common vs. special cause variation to I-MR, X̄-R and X̄-S charts, control limit formulas, and when to use each one. Control charts are one of the core tools used in Six Sigma, quality management, and process improvement methodologies. They are especially common in engineering and manufacturing, but their […]

A Pareto chart is a combined bar and line chart that ranks categories from highest to lowest frequency or impact. The bars show individual category counts on a left vertical axis. The line shows the running cumulative percentage on a right vertical axis, moving from left to right across the categories. Together, they make it […]

Process capability and process performance indices are among the most widely used metrics in Six Sigma and SPC — and among the most commonly misunderstood, even by experienced engineers. Cp, Cpk, Pp, and Ppk all compare process variation against customer specifications, but they answer fundamentally different questions. This article breaks down exactly what sets them […]

Almost every quality problem you will ever face can be analyzed with at least one of the seven basic quality control tools. These tools form the foundation of process improvement in Lean Six Sigma, and the histogram is where the series begins. What Is a Histogram? A histogram is a bar chart that shows how […]

The tool that feeds the histogram — and every other quality tool — at its source. The check sheet is often the very first step in any quality investigation, and for good reason: it is where good data collection truly begins. What Is a Check Sheet? A check sheet is a structured form used to […]

Statistical Process Control offers a powerful set of tools for monitoring and improving process performance — but only if you start with the right chart. Use the wrong one and you risk missing real process shifts, reacting to noise, or drawing conclusions from data that the chart was never designed to handle. The good news […]

A practical walkthrough of creating and interpreting an Xbar-S (Xbar-Standard Deviation) Control Chart using SIGMADESK — covering subgrouping theory, the Xbar Chart, the S Chart, and how they work together to reveal process stability. In this guide, we’ll walk through how to create and interpret an Xbar-S Control Chart — also known as an Xbar-Standard Deviation Chart […]

A practical guide to the Western Electric Rules — what they are, how they work, and how they help detect hidden process problems in control charts before they become serious. Control charts are one of the core tools used in Statistical Process Control (SPC). They are widely used in engineering, manufacturing, and any other field […]