DC cal source are available, espeically if the only have to be resonable stable and not accurate, with a good meter to compare too.
The tricky part is the AC side. Here a good source for the higher voltage higher frequency can get quite expensive.
As the hardware is still the same, it is not clear if the meter with the 3055 firmware still uses the old 3048 calibration data. It may work, as the HW is still the same and they may use a compatible and maybe the same format. Hower this is not for sure, especially as different cal points are used.
Without suitable cal data some ranges may be quite a bit out.
A reasonable good test would be checking a DC voltages of some 2 V in the 2 and 20 V range and see if both read reasonable (within the accuracy of the 3048) the same. This would test the input divider and here idividual units can scatter quite a bit. So wrong cal data would likely produce different readings.
A similar (maybe even easier) could be done with resistors in different ranges (the very low end may not help here, as the 200 mV and 2 V range likely are done with the ADC internal gain and this is naturally quite close to nominal.
First I'm gunna pull you up for constantly referring to 3048 and 3068 where there are no such models in the SDM range !
![Flogging A Dead Horse :horse:](https://www.eevblog.com/forum/Smileys/default/DeadHorse.gif)
Only SDM3065X, 3055, 3045X and the China version 3055X-E.
As to the bold paragraph above if we look back to the OP in this thread we can see although SDM3045X has ranges 600mV, 6V, 60V, 600V and 1kV the OP's issue was a range relay switching at ~2V and messing with measurements where if we are to believe the datasheet the range relay should've been switching at 6V but no, 3045X range relay behavior more closely mimics the 3055 where instead ranges are 200mV, 2V, 20V, 200V and 1kV.
This alerted me to SDM3055X-E might equal SDM3045X and only the ranges were different due to different firmware and they may be calibrated as equals with just SW determining the model #.
That China don't have SDM3045X further points to them having the same HW and as this seems so they are very likely to be calibrated equally.
Another range switching data point might be needed to prove 3045X = 3055X-E beyond reasonable doubt.
Unless evidence to the contrary arises I believe we can say these 2 models share the same HW and calibration procedures.