The dead time of a signal in a controlled system between the measurement of a variable in a process and making the appropriate controlled adjustment, and seeing some effect due to that adjustment arising solely from the finite speed of the propagation of the signal. For example, it may arise from the measurement of temperature of a flowing fluid in a pipe located downstream some distance from a heat exchanger being controlled. Most in-line chemical analysers such as gas chromatographs take time to return a value once a process sample has been taken and can lead to a dead time.