When Lower Uncertainties are Needed

Primary SPRTs are constructed in such a way that the platinum wire coil is free to expand and contract without strain. The flipside of the performance benefit is that the SPRTs are very fragile and require very careful handling. It has been said that if you can hear that you have put an SPRT down on a hard surface you have probably damaged it! Primary SPRTs need the most care, secondary or working SPRTs whilst still needing care are less prone to mechanical shock and can still be calibrated to low uncertainties, typically 0.001 °C at 0 °C and 0.006 °C at 660 °C.