Well thanks for your answers. They are really helpful. So this what I'm getting so far...

I thought because Regular flex is different from one shaft from the others, The industry invented the Frequency Meter to find the real flex of a shaft. But.... Frequency meter does not measure the stiffness of a shaft. Thus it does not tell what the real flex of the shaft.

So I'm thinking my Club Fitter used the Frequency meter to show me nothing. He said my shaft frequency is blablabla during the fitting session. It does not help at all knowing the frequency of the shaft. Is it regular flex? Is it stiff flex? it's just a number....