Frequency error of WSPR reporters during the 8-9 september night on 80m

You may have a look at
The good news is that a large majority of reporters are within +/3Hz and has a good frequency stability.
You can see how I calibrated my TRX before/after the night.

If you wonder why is the frequency calibration important:
Just because it allows the whole 200Hz band to be used and not only the center part, which is often saturated.