The FSM is designed to allow the accurate measurement of loop field strength within an area covered by a hearing loop system. The FSM has many features which make it ideal for surveying and periodically testing induction loop installations. The LOW range setting is provided for measuring cross talk between loop systems and interference from mains equipment such as lighting, dimmers and computer equipment. An "A weight" filter is provided allowing measurements of the audio as the loop is heard by the human ear. This also rejects power hum, allowing accurate assessment of loop installations in areas of high electrical noise.