Electromagnetic field sensors play an important role in determining emissions and immunity of any kind of electronic device. In order to establish if the behaviour of the instrument under test is acceptable, the measurements performed with the sensors must be compared with the current limits and regulations. To ensure that the results obtained with different sensors in different testing environments are reliable and comparable, the sensors must be calibrated by laboratories that are accredited by a national resource. TESEO s.p.a. is one of the laboratories in Italy certified to calibrate electric field sensors, and it employs both a TEM and a GTEM cell, depending on the required frequency range.