Abstract: A radiation pyrometer assembly and method for sensing the temperature of an elongate body, such as metal strip, moving longitudinally in the direction of its length includes a spray gun which deposits a narrow stripe of black paint of a uniform emissivity, upon one surface of the strip as it moves towards a temperature sensing station. The sensing station includes a calibration radiation pyrometer arranged to view the black stripe once the temperature of the stripe has reached the temperature of the strip. The accuracy of the apparatus may be improved by the provision of a process control radiation pyrometer directed to the opposite, unpainted surface of the strip the combined readings from the two pyrometers allow the correction of otherwise unpredictable errors in the temperature of the strip.