SPC (Dev) graph - Y-Axis inexplicably distorted in copy of Same Visual and copy of same Table

[F_Reh]

Good Morning,

I have the following SPC (Dev) graph, based on PBISPC_DEV (Version: 1.4.4.20). It is importing fresh data from SQL-Code:

Neither field is a Measure, and they are also non-Summed (I refer to above graph as the 1st version).

I want to make a second version of the same visual, which is based on copy of the same data set from an Excel file (i.e. static), but in this case the Y-Axis gets inexplicably distorted:

Like the 1st version, both fields used in the 2nd version are NOT measures but I noticed that the X-Axis's field here is in Date Hierarchy form (if that is the cause of the issue ?).

Kindly advise how I can resolve the Y-axis of the 2nd version.

[v-hashadapu]

Hi @F_Reh , Hope you're doing okay! May we know if it worked for you, or are you still experiencing difficulties? Let us know — your feedback can really help others in the same situation.

[v-hashadapu]

Hi @F_Reh , hope you are doing great. May we know if your issue is solved or if you are still experiencing difficulties. Please share the details as it will help the community, especially others with similar issues.

[F_Reh]

Unfortunately the issue still persists in spite of

1) Using YYYYMM directly:

2) Using Don't Summarise and Non-text fields for both X and Y axises:

[v-hashadapu]

Hi @F_Reh , Thank you for reaching out to the Microsoft Community Forum.

I think the distortion happens because the PBISPC_DEV visual interprets Excel date fields differently than SQL date fields. Excel stores dates using its own serial system and when Power BI imports them, those values can shift slightly or come through as DateTime. The SPC visual then reads the X axis as unevenly spaced, which makes it stretch or flatten the Y axis and miscalculate the control limits. That’s why your SQL based chart looks correct while the Excel-based one appears distorted, even with identical settings.

Avoid using a Date column as the ID Key altogether. Instead, create a numeric index such as YYYYMM_Num = YEAR([YYYYMM]) * 100 + MONTH([YYYYMM]), set its type to Whole Number and choose Don’t summarize. Use this field in the SPC visual’s ID Key (Date) slot and sort your table by it. This guarantees a consistent, evenly spaced X axis and identical scaling to your SQL version.

If you really need to keep a Date axis, you can set the X axis type to Continuous and disable label concatenation but the custom SPC visual isn’t fully stable with Date fields across different data sources. 

[v-hashadapu]

Hi @F_Reh , Thank you for reaching out to the Microsoft Community Forum.

@Ritaf1983  is correct, Power BI visuals apply aggregation by default and choosing Don’t summarize can display individual data points. They also rightly noted that ensuring the fields used are of numeric type (not text) is essential, because text fields can trigger unexpected summarization or plotting behaviour.

The main factor behind the distorted Y-axis lies in how the X-axis field is being used. In the second version, the field YYYYMM is being interpreted as a Date Hierarchy rather than a single continuous field. This causes Power BI to group data automatically, changing the scale and aggregation of the Y values. The fix is to remove the hierarchy and instead use the base YYYYMM field directly, not its Year/Month breakdown. Once this is done, and both columns are set to numeric types with Don’t summarize applied, the SPC visual will behave consistently with the first version.

Thank you @Ritaf1983  for your valuable response

[Ritaf1983]

Hi @F_Reh 

Usually, in Power BI visuals, it’s not possible to display each individual data point — some form of aggregation on the Y-axis is always applied (for example, Sum, Average, Count, etc.).

However, based on the screenshots you shared, it seems that your chart manages to display raw values without aggregation. This suggests that the “Don’t summarize” option is enabled.
Keep in mind that this setting can be controlled in two ways:

From the visual itself – by selecting the field on the Y-axis and choosing Don’t summarize.

From the column settings in the data model – by changing the default summarization to Do not summarize.

If the same setup doesn’t work with another dataset, verify that the field’s data type is Decimal Number (not Text) and that the summarization setting is consistent in both cases.

If this post helps, then please consider Accepting it as the solution to help the other members find it more quickly