Figure 3.3 shows how the output varies with time. Initially, at time t = 0,
the output is zero. It then rises to 0.63 of the steady state value after l z,
then 0.86 of the steady state value after 23 and 0.95 of the steady state
value after 3z. After 4z the output is effectively at the steady state value
of k, the exponential term in the above equation becoming zero as time t
tends to infinity.