= Thermocouple reference junction
{title2=$T_c$}
The <thermocouple reference junction> is the connection region where the two thermoelements meet the measurement leads. In ordinary <copper>-lead wiring there are two material transitions, A–Cu and B–Cu, rather than a second welded A–B junction. They must have a common known <temperature> $T_c$ for the simple expression $E(T_h,T_c)$ to apply. An ice-water <heat bath> can establish a nominal $0\,{}^\circ\mathrm C$ reference; <cold-junction compensation> instead measures $T_c$ locally. The word “cold” describes the reference role and imposes no requirement that $T_c<T_h$.
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