Abstract: A method and circuitry for the pyrometric measurements of temperatures of graphite tube atomizers for flameless atomic absorption spectroscopy over very wide temperature ranges of, for example, 100.degree. C.-2700.degree. C. independently of the emission factors of the various graphite tubes. The heated tube is measured by a radiation pyrometer which has a very wide temperature measuring range but with an accuracy that is affected by tube emission factors and is also measured by an independent measuring system which is accurate independently of the emission factor at some particular elevated temperature. When the graphite tube reaches that elevated temperature, the output signals of both systems are mixed to produce an error signal that is used to accurately calibrate the pyrometer circuitry. Since it has been found that the percentage variation of emission factor is independent of graphite tube temperatures, the pyrometer will now produce accurate measurements over a very wide temperature range.