Some days ago, I had problems tuning the PID algorithm in my code, then I came across this virtualization tool. This was the tool that attracted me the most in code warrior but unfortunately I'm not able to use it. I want to see how my variable 'say correction' varries when I give a step input to error. This way I will be able to find the limits of my variable and how my variable responds to step input.. PID - http://www.engin.umich.edu/group/ctm/PID/PID.html The problem is that whenever I enter a variable in the graph tool it does not respond and nothing on the screen change. I also made the variable global but in vain. I have added attachments to depict the situation..