But I don't see why I shouldn't try ...
I has buying an CEM 9979 that finally I managed to return it . As a good thing has a calibration function that you can perform manually , and in case that you screw , you can reset to factory calibration .
Instead I grab this UNI-T at a good price (232 E) but I want to adjust in some points .
For example on 10 volts DC reference that SDM 3065X show as 10.00039 V and Brymen 867s 10.000V, I get 9.997V on UNI-T .
5V - 4.99986V - Siglent , 5.000V Brymen and 4.9990 UNI-T
2.5V - 2.49848V - Siglent, 2.4985V Brymen and 2.4980 UNI-T
VAC - 1.000130 - Siglent, 1.0168 Brymen, 1.0178 UNI-T
L.E. - VAC Mains - Siglent 234.5097VAC, 237.41VAC Brymen and 238.31 UNI-T
If for most of this examples the meter is in specs , for 10V DC it can be adjusted ...
@Thklinge - On CEM 9979 the calibration function was in menu (Setup) and can be performed with the arrow buttons. Maybe on UNI-T there is a secret combination that show calibration menu.
On board there are two ways to talk with the CPU (USB and JTAG) but I don't think that they can be used for calibration . External USB is through IR and I also don't see as a reliable way for calibration ...
So why I am thinking at a secret menu ...