The DF value becomes smaller for each band, and the line on the wide graph is set to the value closest to 1500. This is all you need to do to adjust the reference frequency of the rig. It's easy because you can check it by looking at the DF value and the line on the wide graph.

Now we have a simple, but almost correct calibration.

In addition, when operating the digital mode in WSJT-X/JTDX, once the reference frequency adjustment values are determined, you can then calibrate the rig with WSJT-X, and it is almost perfect.

The values calculated by WSJT-X can also be used by JTDX. You will be able to operate at the correct frequency in all situations, not only in digital mode operation.

If other ICOM rigs are capable of calibrating the reference frequency, the same procedure can be used, and I think it is also possible with YAESU rigs. For example, with the FT-991, just move the REF FREQ ADJ in the menu to the "6" position above.

The discrepancy is only a few Hz to begin with, so there is no need to adjust it, but if you are concerned about it, please do so at your own risk.