https://forum.inductiveautomation.com/t/bug-chart-x-trace-not-showing-correct-values-when-range-zoomed-in/20246

When a pen's value is lower or higher than a chart's Range (i.e. the pen trendline goes outside of the Range bounds), the pen trendline clamps to the min/max value of the Range. The X-trace value also reports the min/max Range value rather than the actual pen's value at that time.