Finally, you need to add the control limits to your chart. If, as in this case, the calculation for the LCL gives a negative result, the LCL on the chart is set to 0 (since you can't have a negative number of defects!).
Add the two lines to your chart and then check your version against the example version, and if necessary, correct any errors before moving on. Remember that the UCL should be drawn in red, and the LCL in black if you're using colour, or they should both be solid lines if you're using black and white only.
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