The range of values shown on a trend chart is not what you expect it to be. For example, the pen's minimum and maximum values are configured as 1 and 100, but the chart shows a range from -50 to 50.
The trend object offers a variety of range options, controlled by options set on the Y-Axis tab. The pen's minimum and maximum values might fall outside of the specified range or outside of the specified scale configured on the Y-Axis tab.
On the Y-Axis tab, check the following:
Options on the Y-Axis tab of the Trend Object Properties dialog box
Keywords: troubleshoot, trend