Bode plot question
I have some problems to understand the initial condition for a straight line approximation to the phase of a bode plot.
For example, we have a straight line approximation to the phase bode plot that starts at -180 degree.
What does it implies in term of number of zeroes and pole at ω=0[rad/s] or initial point.
what if instead of -180 we had 180 degree , 0 degree?
I know that if a plot starts at -90 degree , they must have a pole ((if the constant of the transfer function is positive),
and a zero if the initial phase is 90 degree (if the constant of the transfer function is positive).