The Trend Pens side bar item is used to select the pens which are displayed on the chart. It is also used to select the pen scale which is displayed on the chart.
Trends Pens contains a list of pages which belong to the page that is currently selected. For each of the pens in Trend Pens there is a radio button and a checkbox.
If the radio button of a trend pen that is not selected is pressed then then the pen scale of this pen is displayed on the chart.
If the radio button button of a trend pen that is selected is pressed the pen scales on the chart is displayed. If a pen's checkbox is checked in Trend Pens the pen is displayed in the chart. If the pen's checkbox is unchecked in Trend Pens it is not displayed in the chart.