How to deal with inaccurate thermocouple temperature?

How to deal with the temperature deviation of thermocouples?
There are many manufacturers that produce thermocouples, but few of them can really understand thermocouples. There are also many non-professionals who are discussing this issue. In fact, this problem can be solved through the following methods:
1. First, determine whether the thermocouple and the instrument are correctly connected, and whether the instrument scale is set correctly
2. Use a multi-function multimeter to measure the potential value of the thermocouple. Use a mercury thermometer or other thermometer in the natural space as a comparison to convert the potential value of the thermocouple. If there is no scale, ask me for it. See how much the temperature difference is? Is it within the tolerance? Exceeded. How much more should it exceed? Note: This temperature measurement is only for reference, because there are many other factors that affect temperature deviation. See what the deviation requirement is on site? If it is too high, it must be sent to a reputable organization for calibration and testing (calibration and verification are different)
3. Check whether the material of the thermocouple matches the material of the supplementary wire?
4. Check separately: first check the thermocouple problem, then check the instrument problem, and then check the supplementary wire problem.
5. Whether the positive and negative poles are connected in reverse, make sure they are connected correctly.
6. Temperature tolerance that affects the thermocouple: Is the welding firm? What method is used for welding? Electric welding? Argon arc welding? Or other methods? Is there any slag inclusion? Porosity? Can it be cleaned? Can it be annealed? .