The Power Chart is configured entirely from a script. For each pen, an axis with a fixed range is created. The low/high limits come either from a configuration table or from the tag’s EngLow/EngHigh properties. Before building, props.axes and props.pens are reset to []. The pen’s axis is set to the same name as the axis.
Take a trend with a fixed Y axis range of -1 to 10. When we open it on the last 24 hours, the axis shows -1 to 10 as expected, since the tag has been at -1 all day. But when the tag value is 9 and we switch the chart to realtime with a window of the last minute, so that only the value 9 is visible, the Y axis changes to roughly 8.9 to 10. If the visible window also contains lower values, for example 24 hours with both 0 and 9 in view, the axis stays at -1 to 10. So the fixed range only seems to be ignored when all the visible data is near the top of the range.
I already tried converting min and max to float, hardcoding 'min': -1.0, 'max': 10.0, and switching interaction.mode from panAndZoom to xTrace. None of these changed the behavior. The 8.3 documentation lists only auto, min and max under axes[].range, so i don't think a property is missing.
Is this expected behavior or a bug? And is there a way to keep the Y axis truly fixed, regardless of the visible data?
