Zeros and Poles with respect to stability

[stanford]

I'm trying to grasp the idea of poles and zeroes.

LHP: -20dB/dec
RHP: unstable

for zeros, if they are near the dominant poles, I know it's bad for phase margin but what is the difference between RHZ and LHZ?

 

[stanford]

Anyone know the difference between RHZ and LHZ?

 

[albbg]

The location of the zeors on the plane doesn't affect the stability.