how to draw nyquist plot by hand

i have tried the book of nise and diazo to understand the process of drawing nyquist plot but cant understand anything!
i have tried many sites also , but it does not help me much.. can any one suggest me anything about that ???? please please help me

Hi there,

What are you trying to do, work out the Nyquist Criterion?

The Nyquist plot is a diagram of the phase and gain versus frequency of a system plotted on one line. It shows the phase as the angle and the magnitude as the distance from the origin of the plot. You measure or calculate the phase and gain of the circuit or system and then generate the plot. **broken link removed** is a discussion of how to draw them.

So what is your question about this process?

i dont underasatnd why do u need it?when u can easily calculate it