Trendlines are lines drawn on your graphs. You can specify the starting and ending positions of these lines as well as the graph type. If trendline markers are turned on under Options / Markers your trendlines will be drawn. Trendlines can be assigned to either a specific investment or to your portfolio. Investment based graph types (like Share Price) can display investment trendlines. Portfolio based graph types (like Portfolio Value) can display portfolio trendlines.
Portfolio based trendlines are stored in your portfolio with File / Save Portfolio. Investment based trendlines are stored with the investment using File / Save All Investments.
The easiest way to add a new trendline is to go to the graph where you would like to add a new trendline, and hold down the Shift and Ctrl keys while drawing the trendline with your left mouse button. While drawing the trendline the starting/ending points as well as the annualized yield will be displayed in the status bar. Once a trendline is created you can easily view the data for that trendline by positioning your cursor over either end of the trendline. The data will be displayed in the status bar.
You can use this dialog ( Edit / Trendline... ) to add, edit, or delete trendlines for any open investment or for the portfolio. When adding or editing a trendline you will be presented with the Trendline Dialog.