Function|Add menu item. A new function is added to the end of the
function list at the right hand side of the Plotter main window.
To delete a particular function, click its edit box, and
then chose the Function|Remove menu item. If you
try to remove a function when there isn't one selected, then the last function
in the list is removed. You can clear all the functions
from your graph using the Function|Remove All
menu item.