Accuracy of temperature sensors is how close the sensor output is to the physical temperature being measured. There are international tolerance standards such as IEC 60584-1:2013 and IEC 60751:2008 which define the tolerance bands of temperature sensors. Often small inaccuracies are tolerable but temperature sensor calibration can be conducted to further prove the accuracy of a sensor, or batch of sensors.
What is IEC 60584-1:2013 standard?
IEC 60584-1:2013 specifies reference functions and tolerances for thermocouples (Types R, S, B, J, T, E, K, N, C and A). Temperatures are expressed in degrees Celsius based on the International Temperature Scale of 1990, ITS-90 (symbol t90), and the EMF (symbol E) is in microvolts.