problem with correct frequency units using pwelch or other spectral estimate functions in matlab

I understand that when calculating a spectrum with pwelch the sampling frequency is given by the input variable fs

Assuming I have a monthly time series X of length T = 120 [months] (12 years):

length(X) = 120

Now I would like to calculate a spectrum and get a frequency vector with unit [cycles/year]. Which fs do I have to choose to get the correct output in the frequency vector or plot?

pwelch(X,[],[],[],fs)

[a b] = pwelch(X,[],[],[],fs)

Thanks!!!

Answer 1

[Rick Rosson]

fs = 12;      % samples per year