How to know the exact cutoff frequency of a waveguide?

I've simulated a simple rectangular waveguide (TE10 mode) in HFSS with a frequency sweep. I want to know the exact cutoff frequency of the waveguide (I know that it is analytically c/2a). Where can I find that value exactly calculated by HFSS? You can approximate the value by watchin the gamma constant in frequency domain, but I need the exact value.

Thank you very much.

Really nobody knows my question?

I think you can change output format of the data.If you watch the data in a table ,you can see the cut-off frequency easily.

The amount of attenuation per length that a cuttoff waveguide has is given by an equation for the propagation constant's real part. You have to curve fit the data to that equation. Since attenuation near cuttoff is gradually increasing with decreasing frequency, you will not have an all or nothing type of situation for attenuation vs frequency.

HFSS gives prop constant. From imaginary part of prop constant and the simulated frequency, the exact cutoff can be calculated. The formula to do so is given in many em books like Cheng's Field and wave electromagnetics