Details the performance criteria and other requirements for portable battery or mains ultrasonic flaw detectors using A-scan display, employed for manual ultrasonic examination with single or twin crystal probes of nominal frequency in the range 1 to 5 MHz, but not including probes generating short pulses. Special requirements for equipment incorporated into automated systems, equipment employing B-scan or C-scan display or equipment using non-linear displays or RF-burst transmitter pulses are not included, except that guidance is given concerning RF, rectified and d.c. proportional signal outputs.