Calculated column or measure depending on parameter

You're correct; Power BI does not allow measures to be placed directly in the Legend field of a chart visualization. To achieve the desired result where you can classify the errors into faulty (1) or non-faulty (0) and visualize the proportions in a pie chart, you can follow these steps:

1. Create a new column in your data model that calculates the classification based on the tolerance value. This column will be a calculated column, which is static but is necessary to achieve this specific requirement. You can create it using DAX in Power BI's Data View:

Classification = IF(Table1[err] > [Tolerance], 1, 0)

1. Here, [Tolerance] should be replaced with the parameter or slicer that allows the user to set the tolerance value.

2. Next, create a measure to calculate the count of faulty and non-faulty parts. This measure will use the calculated column you created in the previous step:

Faulty Count = SUMX(Table1, [Classification])
Non-Faulty Count = COUNTROWS(Table1) - [Faulty Count]

1. Finally, create a pie chart visualization. Place the "Faulty Count" measure in the Values field and "Non-Faulty Count" measure in the Values field. You can also add a legend to the chart to distinguish between faulty and non-faulty.

Now, when the user changes the tolerance value using a slicer or parameter, the calculated column will dynamically update based on the tolerance value, and the pie chart will display the relative proportions of faulty vs. non-faulty parts based on the classification.

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