Period Comparison Chart+
Period Comparison Chart+ lays repeated time periods on top of each other, such as today, yesterday and last week, so you see at once whether the current period behaves like the earlier ones. A summary table next to the chart gives the exact numbers for every period.
Overview
Watch the demo
See Period Comparison Chart+ in a practical PI Vision workflow.
When to use it
Use Period Comparison Chart+ when you need to:
- Compare a day, shift, week or month with the periods before it.
- Compare the same weekday or the same month across weeks or years.
- Show how far the current period is above or below a reference period.
- Keep a known good or known bad period on screen while the display time moves.
Choose Combo Chart+ when the question is what happened at absolute clock time, or when the series are not repeated periods of the same measurement.
Before you begin
- Use numeric time-series data: a PI point or an AF attribute with numeric values.
- The archive must hold history for every period you compare. A period without history stays empty.
- Set the display time range first. It decides the first period, and every other period is built from it.
Add and set up the symbol
- Select Period Comparison Chart+ in the PI Vision symbol gallery.
- Drag a numeric data source onto the display.
- In the time bar, set the range to the span you want to compare, for example the last 8 hours.
- Right-click the symbol and select Configure Period Comparison Chart.
- Under Data Retrieval, set Mode to Interpolated and Interval to 15 minutes.
- Under Summary Table, set Show to ON.
- Close the pane. The chart shows the last 8 hours and the 8 hours before them, drawn on one axis that counts the time elapsed since the start of each period. The table below lists both periods.
Common tasks
Compare one day with the day before
Use this for a daily review: is today running like yesterday? The anchor period is the calendar day that contains the end of the display time range. An end time of exactly midnight belongs to the next day, so end the range at 11:59 PM to analyze a finished day.
- Set the time bar to the day you want to analyze.
- Right-click the symbol and select Configure Period Comparison Chart.
- Under Layers, set Period Type (1) to Calendar.
- Set Count (2) to 2, the number of periods to draw.
- Set Duration (3) to 1 Day.
- Under Data Retrieval, set Mode to Interpolated and Interval to 1 hour.
Each day is drawn from 00:00 to 23:00 and labeled with its date. The first period in the list is the one you selected, and the next is the day before.
Compare the same weekday over several weeks
Use this when production follows a weekly pattern and a comparison with yesterday would mislead.
- Start from the setup in Compare one day with the day before.
- Under Layers, set Shift By (1) to Calendar.
- In Offset (2), enter 1 and select Week.
- Set Count to 4.
- Set Highlight First (3) to ON. The first period stays fully colored and the others fade.
The chart draws the selected day and the same day in each of the three weeks before it. Labels such as Oct 8 (-1w) name the offset.
Compare each month with earlier years
Use this for seasonal or year-over-year views. Set the time bar to cover the current year.
- Under Layers, set Period Type to Calendar, Duration to 1 Year and Count to 3.
- Under Data Retrieval, set Mode (1) to Interpolated.
- Set Interval (2) to 1 Month.
- In the data sources section, set Series Type to Bar.
- Under Time Scale, set Type to Discrete, so the months are categories and not points on a time line.
Each month shows one bar per year. A month with no bar has no history in that year, or has not happened yet.
Show how far a period is from a reference period
Use this when the question is "by how much", not "what does it look like". Start from the one-day setup with Count set to 2.
- Under Baseline Comparison, set Show (1) to ON.
- In Mode (2), select Delta for the absolute difference. Percent Delta shows the relative change.
- In Reference (3), select Last Rendered Layer to use the oldest period as the reference.
- Optionally set Overlay (4) to ON to keep the reference curve visible.
Every other period is replaced by its difference from the reference, and the value axis crosses zero. Positive values mean the period was higher. The overlay is drawn on its own hidden scale, so compare its shape, not its height, with the left axis. Band Between Series keeps the original curves and shades the gap instead.
Keep a reference period on screen
Use this when one period, such as a known good day, must stay visible while the display time moves.
- Turn on the summary table under Summary Table.
- In the table, select the pin in the Pin column of the period to keep.
- Move the time bar to another range.
The pinned period moves to a Pinned Layers group and stays in the chart. The other rows sit under Dynamic Layers and follow the new range. Select the red pin again to unpin the period.
Use the symbol
| What it shows | |
|---|---|
| (1) | The first period, drawn in full color when Highlight First is on. |
| (2) | The current-time marker, a dashed vertical line. It appears only while the first period contains the current time. |
| (3) | The tooltip. It lists the value of every visible period at the same position on the axis. |
| (4) | The chart toolbar. |
| (5) | The legend. A hidden period is dimmed. |
| (6) | The summary table, with one row per period. |
- Hover the plot to read the value of every period at the same elapsed time.
- Wheel and drag: the mouse wheel zooms. A drag pans, or draws a zoom box when Box zoom is selected in the toolbar. Zooming moves only the chart and never changes the display time range.
- Toolbar: it holds Pan, Box zoom, Zoom in, Zoom out, Reset zoom, Fullscreen and Download. Download offers PNG, SVG and PDF images and CSV, JSON and XLSX data with one row per plotted point.
- Eye icon: select it in the Visible column to hide or show a period. The change lasts until you reload the display.
- Pin icon: select it in the Pin column to keep a period, as in Keep a reference period on screen.
- No data: a period without history draws nothing. If no period has data, the chart shows an empty-state message.
- Limit lines: when a multi-state is configured for a data source, its limits for the first period appear as dashed lines. They have no row in the table.
- The symbol only displays data. It does not write to the PI System or change other symbols.
Configure the symbol
Right-click the symbol and select Configure Period Comparison Chart. The groups appear in this order. Configure Multi-State is a separate menu command that sets the limit lines.
Style, Title, Legend, Data Labels, Tooltip
| Setting | What it does |
|---|---|
| Style | Theme, Surface, Container Style, Foreground, Background and Font Size change the look. Apply to all symbols copies the theme, surface and container style to every other Vision Library+ symbol on the display. |
| Title | Title and Sub Title show or hide each heading. Alignment places it left, center or right. |
| Legend | Enabled shows or hides it. Position, Placement and Alignment place it, Size fixes its width or height, and Color shows a marker or colors the text. |
| Data Labels | Show prints each value on the plot. Use it on sparse charts only, because labels overlap on dense ones. |
| Tooltip | Show turns the hover tooltip on or off. Pointer selects no pointer, an argument line or a cross. |
Grid, Toolbar, Interactivity
| Setting | What it does |
|---|---|
| Grid | Show turns the grid on or off. Lines selects None, Horizontal, Vertical or Both. Bands shades alternate rows. Border draws the Axes, a Frame or None. |
| Toolbar | Show Toolbar turns the toolbar on or off, every button included. |
| Interactivity | Enable Zoom is the master switch for wheel zoom, drag and the zoom buttons. Drag mode selects Pan or Box zoom as the mode the chart starts in. A viewer's toolbar choice is not saved. |
Layers
| Setting | What it does |
|---|---|
| Mode | Dynamic builds the periods from a rule. Manual lists periods one by one. See the first three tasks. |
| Period Type | Display Time compares the exact range of the time bar with equally long ranges before it. Calendar snaps to whole days, weeks, months or years. Used in Compare one day with the day before. |
| Count | The number of periods, from 1 to 24. Each period of each data source is a series, and the chart warns when it plots more than 12. |
| Duration | The length of a calendar period. Available when Period Type is Calendar. |
| Direction | Past builds earlier periods and Future builds later ones. |
| Shift By | Period steps back by one period length. Calendar steps by the Offset you enter, from minutes to years. Used in Compare the same weekday over several weeks. |
| Periods | The step between periods, in period lengths. Available when Period Type is Display Time and Shift By is Period. |
| Distinguish Layers By | Auto, Color, Line Style or Opacity. Color suits one data source, and line style suits several data sources that already have their own colors. |
| Show Full Historical Periods | Draws earlier months or years in full, even when the first period is shorter. Available when Duration is Month or Year. |
| Highlight First, Other Opacity | Emphasize the first period and fade the others to the opacity you set. |
| Manual layers | In Manual mode, Add Layer adds a row with a name and either an Offset from the display time or a Custom Start Time and End Time. The name appears in the chart and the table. |
Time Scale and Value Scale
| Setting | What it does |
|---|---|
| Type | Timeline draws a continuous time axis. Discrete draws categories. |
| Labels | Scale labels the axis with elapsed time. Range labels it with the date range. Available when Type is Timeline. |
| Show, Position, Title | Show or hide the time axis, place it at the bottom or top, and add its title. |
| Value Scale | Single scale shares one value axis. With several data sources, Multiple gives each its own axis on one plot and Separate gives each its own panel. Use them when data sources have different units. |
| Label Position, Show, Position, Invert Scale, Title | Place, show, flip and title the value axis. |
| Transform | Linear or Logarithmic. Not available while Baseline Comparison is Delta or Percent Delta, because differences cross zero. |
| Scale Range, Ticks, Units | Auto, Database or Custom range, the tick spacing, and the unit text printed in the axis title. |
Data Retrieval
| Setting | What it does |
|---|---|
| Mode | Default loads display-friendly data. Recorded loads the archived events and can return many points on long ranges. Interpolated samples every period at the same Interval so points line up. Summary returns one calculated value per interval. |
| Interval, Sync Time | The sample or summary spacing, and an optional clock time that the intervals start on. Available for Interpolated and Summary. |
| Type, Basis | The calculation for Summary: Total, Average, Minimum, Maximum, Range, Standard Deviation, Population StdDev, Count or Percent Good, and Time Weighted or Event Weighted. Available when Mode is Summary. |
| Start- and Endtimes | Display time range, a Custom time range, or a Duration and offset. The first period follows this range. |
Summary Table and Baseline Comparison
| Setting | What it does |
|---|---|
| Summary Table | Show turns the table on or off. Height (%) reserves a share of the symbol, and 0 means automatic. Columns select Value, Average, Standard Deviation, Min, Time at Min, Max, Time at Max, Count and Sum. The name, visibility and pin columns are always there. |
| Baseline Comparison | Show, Mode and Reference as in Show how far a period is from a reference period. Tooltip Only leaves the chart unchanged and adds the baseline, delta and percent delta to the tooltip. Specific Layer takes a Layer Number in the rendered order. |
| Band Opacity, Overlay Opacity, Tooltip Details | Set the shading, the overlay curve and whether the tooltip lists the difference. |
Data sources
| Setting | What it does |
|---|---|
| Data source list | Selects the data source to edit. Several data sources multiply the number of series. |
| Label, Color | The name in the chart and table, and the data source color. When several periods are drawn, the final color also depends on Distinguish Layers By. |
| Series Type | Line, Area, Bar or Scatter. Use Bar for interval values. |
| Line Shape, Dash Style, Line Width, Marker Size, Markers | Style a line or area series. Step line shape suits states that hold until the next change. |
| Layers | All repeats the data source in every period. Anchor Only draws it in the first period only, which suits a target or a limit. |
Troubleshooting and limitations
| Symptom | Cause | What to do |
|---|---|---|
| A period is missing or empty. | The archive has no history for that period, or the period lies in the future. | Check the data source in PI System Explorer, or select a shorter Duration or a smaller Count. |
| The first period is the wrong day. | In Calendar mode the first period is the day that contains the end of the display time, and midnight belongs to the next day. | End the display time range at 11:59 PM. |
| The chart shows a warning about the number of series. | Periods multiplied by data sources exceed 12. | Reduce Count or the data sources, or hide periods in the table. |
| Lines look noisy. | Data Retrieval Mode is Default or Recorded on a fast-changing point. | Select Interpolated and a longer Interval. |
| Transform is missing in Value Scale. | Baseline Comparison is Delta or Percent Delta. | Switch the baseline to Band Between Series or Tooltip Only. |
| The toolbar is missing. | Show Toolbar is OFF. | Set Show Toolbar to ON. |
Limitation: The time axis is aligned: every period is folded onto the first one, so zooming never changes the display time range.
Limitation: Data sources with different units share one scale unless you select Multiple or Separate under Value Scale.
