#77 FFT should have correct independent variable

[Buenos]

When I do an FFT on a transient sim result waveform, I get a signal frequency spectrum. This spectrum has "number" as the independent variable, instead of frequency. This happens with both fft and dft. The same issue with ifft when converting an AC sim result into a time domain waveform it should display independent variable as time in ns.
Can we implement the independent variable conversion (us <--> MHz) as part of the fft/dft/ifft ?