I have been working on some loops in step 7 which are requiring me to us STL. I asked my local Siemens tech support guy some questions and he said I should purchase SCL. So my question is should I buy the SCL software or should I upgrade my Step 7 Basis to Step 7 Pro? I am told that Pro will come with SCL, Graph and Simulator. Pro is about $500 more than SCL by itself. Is it worth it for Graph and Simulator? What is Graph used for?