Spectral ratio pyrometers due to the components base advances have become cheaper, and now at an average they are half as much more expensive then conventional energy pyrometers with the same metrological characteristics. They are free from most of the energy pyrometers disadvantages. First, they do not need to enter the emissivity coefficient, and secondly they allow you to measure the temperature of small objects that are smaller then the pyrometer field of view at a selected distance. In the third place they allow to measure through glass practically without loss of accuracy, further the measurement result does not depend on the distance to the measuring object. But are they so perfect?