in a method of plotting section images of objects subjected to ultrasonic examination , a section surface of the object is scanned with a sound beam and echoes generated in response to the pulses of the sound beam are converted into echo signals which are plotted on a plotting surface , such as a fluorescent screen or a record carrier , to form a section image . the sound beams scans the section surface at a varying velocity . the pulse repetition period of the sound pulses is varied so that the section surface is scanned with a uniform transverse resolution . in equipment for carrying out the method , the pulse repetition frequency of the sound pulses is controlled by a trigger which generates trigger pulses at times which are functionally related to the scanning movement of the sound beam . the trigger may comprise programmed memory .