I think I've figured it out.
At 5ms/div the FFT disappears, correctly because the sample rate is then too low.
But it comes back when enough sample rate is available - from 2ms.
But earlier it didn't come back and the scope was permanently stuck at 12.5MSsa/s.
So don't play around with it too much...
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
Otherwise, the FFT function behaves in the same way as its big brother, the 4204.
In other words, hardly anything can be set, no different modes, which is a particular pity that there is no averaging.
And what I already noticed in February with the 4204 is also present here.
Generator with wavecombine function, 10Mhz frequency, ch1 10Vpp, ch2 1mVpp 10.1Mhz frequency, 50Ohm termination.
I have done this with another scope with a "flattop" window and it works perfectly.
With Rigol it looks different when you switch from Hanning to Flattop.