UsingTurbocad Mac Delux 9, Under Training, Tutorial Session 2, Creating an Arc using Fillet, you are told to hold down Alt key (in Mac I think they mean the option key) and then click to create the fillet. If you do not use the option key, the fillet is created but a portion of the circle is cut away. I can not understand how the program is deciding what portion of the circle is being cut away. I can do the task but am trying to understand what is happening when I DO NOT use the option key. Can anyone explain what is happening and why?