IEC TR 61948-1:2016(E), which is a technical report, describes test methods of instruments that count and measure the energy of photons emitted by radionuclides in vivo and in vitro without the option of imaging. This includes, for example, well counters and organ probes. Geiger-Mueller counters and dose calibrators are not within the scope of this document. This second edition cancels and replaces the first edition published in 2001. This edition constitutes a technical revision.