To Add or Delete a Trace
1. On a plot, add a y-axis expression.
2. Press Enter. A new plot trace appears. Both of the y-axis expressions are related to the same x-axis expression.
3. If you want the y-axis expression that you added to relate to a different x-axis expression, add another x-axis expression and press Enter. The trace changes accordingly.
Alternatively, repeat steps 1 to 3 starting by adding a x-axis expression.
4. To delete a trace, delete axis expressions that define the trace. You may need to delete expressions on both axes. The trace does not disappear until you evaluate the plot by pressing Enter.