# Nyquist Stability Theorem and Clockwise/Counter Clockwise Encirclements

According to argument principle, if a contour encircles a number of poles and zeros of a transfer function, the number of origin encirclements can be deduced by : N = Z - P

In which N can be both positive and negative which means it can either be counter clockwise or clockwise.

But in Nyquist theorem, most of the time we are only counting the number of counter clockwise encirclements of point (-1,0) with no mentions of possible clockwise encirclements. Why is this?

• Can you add a reference? To my knowledge, I've never encountered such a statement. – useless-machine Jul 6 '20 at 8:47