Gain margin and phase margin expressions from nyquist plots

Virtuoso IC6.1.8-64b.500.27

mmsim 21.10.612

Hi all,

I have run some stb sims and the output log says that the circuit is unstable, but the step response of the transient simulation looks OK (about 30 deg worst case) and confirmed it through a visual inspection of the nyquist plot. I would like to generate expressions that read both phase and gain margin directly from the nyquist plot and store them in my assembler view. Visual inspection isn't an option when simulation hundreds of corners. 

Has anybody implemented this before? Thanks in advance,