UCL calculations limits and graph

Hi KOLD1313 ,

Based on the testing, please try the following methods:

1.Create the sample table.

2.Create the new measure to calculate average.

Average Rate = 
CALCULATE(
    AVERAGE('Table'[Rejects rate]),
    DATESINPERIOD('Table'[Date], MAX('Table'[Date]), -15, MONTH)
)

3.Create the new measure to calculate the std.

Std Rate = 
CALCULATE(
    STDEV.P('Table'[Rejects rate]),
    DATESINPERIOD('Table'[Date], MAX('Table'[Date]), -15, MONTH)
)

4.Create the measure to calculate the ucl.

UCL Rate = 
[Average Rate] + 2 * [Std Rate]

5.The result is shown below.

Best Regards,

Wisdom Wu

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