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Precision Control Chart

It's Easy to Create a Precision Chart in Excel

Healthcare labs use the Precision charts to monitor paired measures. In this data, there are two measurements on the same day. RPD is calculated using the formula shown:

The Precision control chart can be created in two ways:

1. as a Levey Jennings Chart of Relative Percent Difference (RPD)
2. or the R chart of an XbarR chart of the two different measures.

Example of a Precision Control Chart

1. To create a Precision chart of RPD using QI Macros:
• Select your Precision chart data (dates and RPD) in an Excel worksheet.
• Next, click on the QI Macros menu > Control Charts (SPC) > Special (CUSUM, EWMA) and then Levey Jennings Stdev:
  



• Precision chart uses standard deviation to draw the 2 sigma (Warning Limit) lines and the upper and lower control limits.
• Adjust the Y axis to cross at zero and Show the 1-2 Sigma lines using QI Macros Chart Menu. The 2-sigma line is known as the Warning Limit. One point is above the warning limit:
  
  
  
2. To create a Precision Control Chart of the ranges between two measures:
• Select the data (dates and measures 1-2)
• Next, click on the QI Macros menu, Control Charts and then the XbarR chart.
• Use the R chart and discard the X chart:
  

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Why Choose QI Macros Over Other Control Chart Software?