You can add curves for the same set of contracts, but for different periods of time. You can set that period in preferences.
Click a curve button in the lower right corner of the window. Active buttons are orange. A curve line will be added for each button you click.
To add curves from the chart
Place a vertical line on the chart (click in the date/time area, drag to desired location, click again).
That vertical line is represented by a curve on the Yield Curve or Forward Curve window.
To remove curve
Click an active curve button.
You can also right-click the curve identifier at the top left of the window, and then click Remove Curve, like this:
You can also remove the curve by removing the corresponding vertical line or vertical cursor from the chart.
To change symbol
1. Make sure the curve window is selected.
2. Type the new symbol. As you begin to type, the symbol field is displayed, like this:
3. ENTER.
You can also enter a symbol and range. The format is: symbol[low bound:high bound].
For example, EP [-1:2], where -1 and 2 are number of contracts being stepped from the most active one. You can also use a comma or semi-colon to separate the bounds.