Hello,
What modem is in your device? If you are unsure, you can send me the order code and I will look it up.
Since a calculation is needed to calculate the PSU voltage, it could be that the hardware revision of your device has different components, thus a different formula may need to be used. It could also be the case, that it will not be possible to measure the voltage at all.
Best regrads,
DaumantasG