Consider a single CSTR (continuous stirred-tank reactor) with a residence time equal to three hours. A square pulse input of width is defined by , if and if , where is the Dirac delta function and is the unit step function. This Demonstration plots both the CSTR's residence time distribution (RTD) curve and the square pulse input for user-set values of the width parameter . If , one recovers the usual RTD for an impulse input.