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Let’s replace the ice bath with another isothermal block. The new block is at TREF, and because voltmeter connectors are still at Tc temperature,

[VTC] = Sab*(Tx-Tref)

This is still an inconvenient circuit because we have two thermocouples.

Let’s eliminate the extra wire in the negative lead by joining the two isothermal blocks:

Still

[VTC] = Sab*(Tx-Tref)

Now we call upon the law of intermediate metals to eliminate the extra junction. This empirical “law” states that a third metal inserted between the two dissimilar metals of a thermocouple junction will have no effect upon the output voltage as long as the two junctions formed by the additional metal are at the same temperature:

This is a useful conclusion, as it completely eliminates the need for the extra junction.

Again,

[VTC] = Sab*(Tx-Tref),

Where Sab is the Seebeck coefficient for the thermocouple.

Junctions C1 and C2, take the place of the ice bath. These two junctions now become the Reference Junction.