Doug Phillips wrote
Like all endeavors RTFM applies here, very good pdf file instructions.
Non-WSPR users, take a special look at the excellent Appendix C "Frequency Calibration".
Just measured my K3 and found A = -0.5 Hz, B = 0.33 ppm. Very good, isn't it?
Did 3 measurements at 6, 10 and 22 MHz, then fitted a straight line in Excel.
73, Markus