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PQ Systems Knowledge Base 
ST: 4.6.3. Interpret Cp and Cpk
Viewed 11621 times since Thu, Jan 10, 2008
Revision Date: 20050907 The Cp and Cpk indices are the primary capability indices. Cp shows whether the distribution can potentially fit inside the specification, while Cpk shows whether the overall average is centrally located. If the overall... Read More
ST: 4.6.2. Calculate Cpk
Viewed 10873 times since Fri, Nov 9, 2007
Revision Date: 20050907 Cpk takes into account the center of the data relative to the specifications, as well as the variation in the process. Cpk is simple to calculate. The smaller of the two Z values is selected. This is known as Z min... Read More
ST: 4.6.4. Calculate Cpu and Cpl
Viewed 8632 times since Wed, Nov 14, 2007
Revision Date: 20050907 Cpu and Cpl are the Cpk values calculated for both Z values. Therefore, Cpu is: For the example: Cpl is: For the example: From Cpu and Cpl, it is evident that the smaller value for the example is Cpu, which is the... Read More
ST: 4.6.1. Calculate Cp
Viewed 6444 times since Fri, Nov 9, 2007
Revision Date: 20050907 Cp is an index used to assess the width of the process spread in comparison to the width of the specification. It is calculated by dividing the allowable spread by the actual spread. The allowable spread is the... Read More
ST: 4.6. Calculate and interpret the capability indices
Viewed 3662 times since Mon, Dec 10, 2007
Revision Date: 20050907 This step describes the key capability indices. 4.6.1. Calculate Cp. 4.6.2. Calculate Cpk 4.6.3. Interpret Cp and Cpk. 4.6.4 Calculate Cpu and Cpl Practical Tools for Continuous Improvement... Read More
ST: 4.2. Calculate the estimated standard deviation
Viewed 2958 times since Fri, Nov 9, 2007
Revision Date: 20050906 The next stage is to calculate the position of the tails of the distribution that has just been drawn. However, in order to calculate the position of the tails, the standard deviation is required. In this version of... Read More
ST: 1 What is it
Viewed 2689 times since Fri, Nov 9, 2007
Revision Date: 20050906 Capability analysis is a set of calculations used to assess whether a system is statistically able to meet a set of specifications or requirements. To complete the calculations, a set of data is required, usually... Read More
ST: 4.5. Calculate how much data is outside the specifications
Viewed 2575 times since Fri, Nov 9, 2007
Revision Date: 20050907 As indicated in the previous step, some of the distribution is outside the specification limit. The question is, how much? To determine the percentage that falls outside the specification limits, it is necessary to... Read More
ST: 4.5.3. Determining the total percentage outside the specifications
Viewed 2556 times since Fri, Nov 9, 2007
Revision Date: 20050907 The total percentage outside the specification limits or requirements is found by adding the percentage outside the upper and lower specification limits. The total percent of output located outside the specification... Read More
ST: 4 How is it made
Viewed 2353 times since Fri, Nov 9, 2007
Revision Date: 20050906 These steps assume that variables data has been collected over time, and that a control chart and histogram have been completed. The control chart should show no special causes, and the histogram should reveal that... Read More
ST: 3 When is it used
Viewed 2300 times since Fri, Nov 9, 2007
Revision Date: 20050906 Use the standard method for calculating capability analysis when you can answer "yes" to all of the following questions: 1. Is it necessary to understand how the system performs in comparison to specification limits... Read More
ST: 4.4. Draw the specification limits on the distribution
Viewed 2294 times since Fri, Nov 9, 2007
Revision Date: 20050906 Draw vertical lines on the distribution to represent the lower and upper specification limits. In the example, the lower specification limit (LSL) is 0 minutes (on time) and the upper specification limit (USL) is 14... Read More
ST: 4.3. Determine the location of the tails for the distribution
Viewed 2245 times since Fri, Nov 9, 2007
Revision Date: 20050906 The next step is to determine where (at what value) the tails or ends of the curve are located. These values can be estimated by adding and subtracting three times the estimated standard deviation from the overall... Read More
ST: 4.5.1. Find the percentage above the upper specification
Viewed 2245 times since Fri, Nov 9, 2007
Revision Date: 20050907 The first step in determining the percentage above the upper specification is to calculate the Z value for the upper specification. This is found by subtracting the overall average from the upper specification, and... Read More
ST: 4.5.2. Find the percentage below the lower specification
Viewed 2225 times since Fri, Nov 9, 2007
Revision Date: 20050907 The Z value for the lower specification is found by subtracting the lower specification from the overall average, and then dividing by the estimated standard deviation. The Z value for the lower specification is... Read More
ST: 4.1. Sketch the distribution
Viewed 2150 times since Fri, Nov 9, 2007
Revision Date: 20050906 Sketch a picture of a normal distribution. Begin by drawing a horizontal line (axis). Next, draw a normal (bellshaped) curve centered on the horizontal axis. Then draw a vertical line from the horizontal axis... Read More
ST: 2 What does it look like
Viewed 2107 times since Fri, Nov 9, 2007
Revision Date: 20050906 A courier company has set up a team to look at the actual arrival time at customersâ€™ locations to pick up packages, in comparison to the scheduled arrival time. The company guarantees pick up of packages within 14... Read More
ST: 4.7. Analyze the Results
Viewed 1968 times since Fri, Nov 9, 2007
Revision Date: 20050907 The completed analysis for the example is shown below. Calculations: = 2.00 Zupper = 2.00 Zlower = 5.00 Cpk = 0.67 Cp = 1.17 Cpu = 0.67 Cpl = 1.67 Examine the capability indices... Read More

