FFT on continuous fifo data - Is y axis magnitude sum of all samples?
In general the  output of a Fourier Transform is &quot;spectral density&quot;. For a continuous Fourier Transform that's implicit: if the signal in Volts, the unit of the FT are Volts/Hz. For the discrete case, the units are the same but the frequency interval is implicit: it's the sample rate divided by the FFT length.
If you want to extract &quot;physical&quot; meaning from the FFT, you need to watch your scaling. In your specific case it would probably be best to scale both the forward and backward FFT by $1/\sqrt{N}$ since that maintains Parseval's theorem, i.e.
$$\sum |x[n]|^2 = \sum |X[k]|^2$$
which means that total power in the time and frequency domain are the same.