The MacGREGOR Sherlog is a type-approved, ultrasonic testing system for verification of tightness of hatch covers, doors, ramps and windows. Sherlog equipment can also be used to test bulkheads or any openings on board which need to be sealed. It consists of two parts: an ultrasound multi-transmitter and a hand-held detector. The multi-transmitter is placed in the hold in the central position. It produces a uniformly-distributed omni-directional sound field throughout the hold space. The hand-held detector measures the sound energy. The transmitter sound is produced in a narrow frequency band and the detector is tuned to filter out just this band. Thus the inspector, wearing a headphone and reading a digital display, is not hampered by surrounding noise and can positively detect any leak greater than 0 dB.