Thank you for the response. I think what you are saying is that I can't adjust the device itself to output the correct frequency i.e. 1kHz in the drop-down outputs 1kHz.
However, I can change the frequency in the drop-down until the actual output is correct.
If this is the case then may I suggest that a facility to add a correction factor to the frequency would be a useful addition to the program. This would enable a one-time calibration of the frequency and avoid having to enter different figures each time.