if that dont help you can still do some basic checks like measure the power rail voltage inside the device if you can find it, it might be as simple as a bad LDO or something. There is a chance its actually broken, not that it needs adjustment.
One part of the reason why some calibration is not recommended is because.. cheap asses will just "favor" the idea that the calibration drifted, not that there is a problem with the meter.
Software people especially. Reads 2V should read 6? it means add +4 to calibration duh
meanwhile the reference is bad and its providing like 1.5 instead of 2.5v and everything is totally whacked out
A sway bar thing fell off my lawn mower. I stopped for 30 min to find the bolt in the dirt and fix it. I can see the software guy duck walking around with his back at a 45 degree angle to keep the lawn mower steady so he can finish the job
if fluke sees a 30% error in full scale, it means something is FUCKED. They gave you a parts replacement bill