Basically, don't erase/delete anything until you're sure you're done with it. Save the line handle(s) to the lines when drawn; if you want to hide them temporarily, set hL(idx).Visible='off' for those when create the next set (with a new entry in the line handles array so you don't lose the previous, of course).
When you decide you are satisfied and don't want the earlier, then you can delete() those particular line handles and reuse that array element(s).
To go back, delete() the current array entry lines and return the .Visible property to 'on' again.
