Thermal hysteresis of travelling inductance standards

The international comparison CCEM-K3.2018 "Inductance at 10 mH and 1 kHz" is under preparation. To verify the uncertainty claims of the participant institutes, travelling standards of unprecedented level of stability are required. INRIM and PTB characterised several General Radio 1482 inductance standards versus large temperature steps that may occur during air carrier transportation. This work reports on the unexpected thermal hysteresis manifested by these standards which may impact on the uncertainty of the reference value of the K3 comparison.