Hello, I've been studying PID control and I've undestrood many things, but in every source I've read there is no exact definition for what the Integral Time and Derivative Time are. I now know what is the results of setting them high and low—to some extent—and have studied a bit the tuning methods for when you don't have a model for the plant. But exactly what is the Ti? If the integral of the error is always being calculated, then what is the exact definition for it? Same for the Td. Thanks in advance.