Some of your radios not talking to Pi-Star? Try this

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I own a few radios, TYT MD380, Anytone 878, Anytone 578UVIII, Motorola XPR4550, Motorola XPR7550, ICOM ID51A+
Some would talk to my hot spot and some wouldn't, I suspected a frequency issue with my hot spot.
I built my hot spot seven years ago using a Raspberry Pi and a DVMega Raspberry Pi-Hat (GPIO) Dual band board running Pi-Star V4.1.4 Feb
This particular radio board would not work with the embedded SSH Access calibration tool in Pi-Star so I had to come up with a different plan.
Not owning a frequency counter that would accurately resolve down to 100hz I went a different route.
I set up a digital VFO in my Anytone 578 and dithered the frequency +/- until I saw what appeared to be a -450hz offset before showing up in Pi-Star.
Going further, I built 10 private channel talk groups in my Motorola XPR7550 and labeled them +500hz down to +100hz and -100hz up to -500hz and offset my hot spot radio frequency in each talk group by the same amount.
I then moved away from my hot spot several hundred feet and opened up the Pi-Star dashboard on my smartphone which is connected to the home WiFi.
then selecting each offset and keying them up while watching the RF activity on the Pi-Star dashboard screen I came to a similar conclusion of -450hz.
I then went into "Expert" mode in Pi-Star and went to the Modem menu and put +450 into the RX and the TX offset fields respectively and now all of my radios are reliably connecting into Pi-Star.
I then loaded a previous version of my XPR7550 software back in which removed the experimental talk groups.
What I have learned:
Apparently the threshold for reliable communication between radios and the hot spot is +/- 500hz
Always suspect the hot spot first, why? Because most higher end radios use TCXO and most hot spots do not, so they drift.