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Sketch a picture of a normal distribution. Begin by drawing a horizontal line (axis). Next, draw a normal (bell-shaped) curve centered on the horizontal axis. Then draw a vertical line from the horizontal axis through the center of the curve, cutting it in half. This line represents the overall average of the data and is always located in the center of a normal distribution. Label the line with the value for the overall average and its symbol. The value of the overall average in the example is 10.00 and the symbol for the overall average from the chart is . The example completed through this step follows.
The above article is an excerpt from the “Operational definition” chapter of Practical Tools for Continuous Improvement Volume 2 Statistical Tools.