Roger,
I am going to guess that your questions are why the results of a scan with the Antuino do not match either the Rig Expert 230 or a NanoVNA when scanning the same antenna.  The short answer could be calibration. 

The longer answer could be that the results of the Antuino can vary with the Span setting.  The limitation of the Antuino when scanning an antenna for SWR is that if the span is set much above 1MHz then there could be "Skipped" sections that are not measured.  The behavior is due to the screen horizontal resolution (128 dots), and to keep the scan time sorter the fact that the sampleing starts with the Center Frequency - 1/2* Span Setting and then samples every Span Setting/128.  At large spans there can be sections of the band that are not measured.  One of the SWR low points could be in the section of the band that is not being measured.

I would suggest that you test with the span set for 1 MHz and see how that compares with a similar scan on the other two devices.

It would also help us help you if you could be more specific on what the differences are.  Example:  The minimum SWR reported by the Anuino is much higher than the------- or the reported minimum is 100KHz different.

73
Evan
AC9TU