The closed-loop system, whose open-loop transfer function
is *GH*(*s*) is stable if and only if *N* = -*P* ≤ 0 ,
where:

•*P* ≡ number of poles of *GH*(*s*) in the right-half plane
(*P* ≥ 0)

•*N* ≡ total number of clockwise encirclements of the (-1,0)
point (*GH*(*s*) = -1) () in the *GH*(*s*) plane

If

the number of zeros

in the right-half plane is determined by

If

the (-1,0) point is not enclosed by the Nyquist stability plot. Conversely

if the region to the right of the contour in the clockwise direction does not include the (-1,0) point.