Your book is excellent! I am having trouble understanding the "Two Point Method" you mentioned. It seems you mark the 28.3% and 63.2% points on the process variable ramp. I just don't know what to do after that. Do I multiply this time by 1.5, and use the result as the time constant? Do I then take the whole time value from the Step Change to the 63% PV, and subtract the above calculated time constant and use what is left as the Lag Time?