Mark,
If you are just measuring SWR on HF antennas you can do the calibration from 1 to 30 MHz. on the CH0 SMA connector and store it in one of the memory slots 1-4. Then just recall it after powering up. You then use Stimulus to zoom in on the band of interest (40m, 20M etc.) and the NanoVNA interpolation routine will take care of it. Attached is a file showing what happens with different calibration settings when measuring SWR. Note: I am referring to SWR measurements ONLY here.
Roger
Roger Need