Hi,
I'm not sure but can suppose that this technique is based on measurement of thermocouple reply when you place it in 9 substances with known temperature.
For example usually we use 2 points - melting of ice (0 C) and water boiling (100 C). But you can add more points to calibrate your thermocouple, for example, melting points of some metals (lead - 327.5 C, Bismuth - 271.4 C, aluminum 660.3 C, copper - 1085 C, etc.). This will allow you to make calibration accurately and will spread the range of correct measurements.
Good luck.
Oleg Chutko.
