only had to be performed once for all time, and for all materials; for any other material, the absolute Seebeck coefficient can be obtained by performing a relative Seebeck coefficient measurement against a standard material. A measurement of the Thomson coefficient , which expresses the strength of the Thomson effect, can be used to yield the absolute Seebeck coefficient through the relation: , provided that is measured down to absolute zero. The reason this works is that is expected to decrease to zero as the temperature is brought to zero—a consequence of Nernst's theorem. Such a measurement based on the integration of was published in 1932, though it relied on the interpolation of the Thomson coefficient in certain regions of temperature. Superconductors have zero Seebeck coefficient, as mentioned below. By making one of the wires in a thermocouple superconducting, it is possible to get a direct measurement of the absolute Seebeck coefficient of the other wire, since it alone determines the measured voltage from the entire thermocouple. A publication in 1958 used this technique to measure the absolute Seebeck coefficient of lead between 7.2 K and 18 K, thereby filling in an important gap in the previous 1932 experiment mentioned above. The combination of the superconductor-thermocouple technique up to 18 K, with the Thomson-coefficient-integration technique above 18 K, allowed determination of the absolute Seebeck coefficient of lead up to room temperature. By proxy, these measurements led to the determination of absolute Seebeck coefficients for all materials, even up to higher temperatures, by a combination of Thomson coefficient integrations and thermocouple circuits. The difficulty of these measurements, and the rarity of reproducing experiments, lends some degree of uncertainty to the absolute thermoelectric scale thus obtained. In particular, the 1932 measurements may have incorrectly measured the Thomson coefficient over the range 20 K to 50 K. Since nearly all subsequent publications relied on those measurements, this would mean that all of the commonly used values of absolute Seebeck coefficient (including those shown in the figures) are too low by about 0.3 μV/K, for all temperatures above 50 K. Seebeck coefficients for some common materials In the table below are Seebeck coefficients at room temperature for some common, nonexotic materials, measured relative to platinum. The Seebeck coefficient of platinum itself is approximately −5 μV/K at room temperature, and so the values listed below should be compensated accordingly. For example, the Seebeck coefficients of