Introduction: Control Chart XmR
The most effective way to detect signals of change in your KPI is to use a Control Chart
The Control Chart helps you to determine if your processes are in control. When your measurements meet certain criteria (see below), an indicator immediately tells you something is going on. This helps you to determine the source of this variation.
The Control Chart XmR consists of two charts: The upper chart (X-Chart) displays the data points over time together with a calculated average. The calculated average is then used to calculate the Upper and Lower Control Limits (UCL and LCL). The lower chart displays the Moving Range (mR-Chart) with its Average and Upper Control Limit. The mR-Chart can be hidden.
The rule set for the detection of signals is customisable. By default it is:
- A point is outside the control limits
- 7 points in a row are above or below the center line
- 10 out of 12 points are above or below the center line
- 3 out of 4 points are closer to the UCL or LCL than the center line
You can add your own target line, to see how your process is doing compared to a certain goal. If you have determined the center line and control limits separately, you can easily add these to the visual as well.
Key features of the Control Chart XmR are:
- Switch between standard and trending XmR: processes with natural trends (continuously increasing or decreasing) can be analysed with the Trending XmR function.
- Highlight signals: Detected signals can be indicated below the chart, and the measurements themselves can be coloured in a separate colour.
- Work on various time scales: choose the appropriate time scale for optimal analysis, ranging from seconds to years;
- Format the objects: All lines, markers and axes can be formatted independently, and support theme settings;
- Selection & Highlighting: Like in standard Power BI Charts you can make use of the Selection & Highlighting functions within the Control Chart XmR;
- Context menu: Like in standard Power BI Charts you have access to the context menu to include and exclude data points;
- Full tooltip support: Besides the default Tooltip behaviour (show the value of the element you hover) you can also add additional fields to the tooltip.
- Full Bookmark support: like any of the standard visuals the Control Chart XmR supports Bookmarks.
How to use: the Fields pane
To use the Control Chart XmR, you need to have a dataset with at least a date-field and a numeric field. The available buckets are:
- Date: Here you add the field you want to use as your x-axis. Make sure to use the actual dates instead of the Date Hierarchy.
- Actuals: This field contains your measurements.
- Target values: This field contains your target points, which can be shown as a line or a sequence of markers.
- Central Line: The Central Line will be calculated automatically. You can add your own Central Line by including it in this bucket.
- Control Limits: The Control Limits (or natural process limits) are calculated automatically, but can be added here. You can add a two fields to this bucket: one for the lower limit and one for the upper limit. The order of the two doesn’t matter
- Signals: An indicator will be shown in the chart as soon as this field is non-empty. You can have an indicator for every point in your Date field.
- Tooltips: The fields added here will shown in the tooltip when the user hovers a specific data point.
How to use: the Format pane
The Control Chart XmR comes with many of the standard Power BI formatting options. Titles, axis labels, line and markers appearance, etc.: it’s all there.
This section focusses on the features that deserve a bit more attention, sorted per card:
The X-axis card
- Date type: With this option you can define the formatting of the date labels on the X-axis. The options range from Years to Seconds. Note that making changes to this option does not invoke any changing to the grouping of your data.
The Data Colors card
- Actual: this defines the color of the Actual line, and (if enabled) the markers on that line.
- Actual (outside Control Limits): for highlighting purposes, you can change the color of the Actual markers when they fall outside the Control Limits bandwidth. The Actual line itself will not change color when outside the control limits.
The Data point card
This card contains all options for formatting the lines and markers in both parts of the chart.
- Show CL as step: in some case it makes sense to show the Central Line stepped. Toggle this option on to do so.
The Show mR chart card
Toggle this option on to see the mR chart, displaying the moving Range.
The Calculation card
Here you will find the options that affect your analysis the most. You can change the number of points considered for the average and each rule, and more:
- Auto recalculation: Turning this option on will induce a recalculation when Rule 2, 3 or 4 (if enabled) is violated. A new center line and control limits is calculated. Then the option is turned off, then the center line will be based on the points as defined by the parameter Data values for Average.
- Trending XmR: Turn this option on if you have a measurement with a naturally increasing / decreasing behaviour. All rules remain the same, but the CL becomes a slope which best fits your data.
- Show signals: When one of the rules is violated, then a small indicator will be shown in the chart. In case you have add a field to the Signal bucket, then non-empty values will also result in an indicator. Hover over the indicator to see which rule has been violated.
- Data values for Average: This option determines how many points are used to calculate the center line and control limits. Make sure that this value is lower than the number of data points you have.
- Rule 1: A point is outside the control limits (doesn’t invoke recalculations)
- Rule 2: n points in a row are above or below the center line. The n can be changed, default is 7.
- Rule 3: n out of n+2 points are above or below the center line. The n can be changed, default is 10.
- Rule 4: n out of n+1 points are closer to the UCL or LCL than the center line. The n can be changed, default is 3.
For any questions or remarks about this Custom Visual, please contact us by email at Nova Silva Support or visit the community forum.