This locator is ideal for locating aluminum, brass, copper, iron, lead, nickel, tin or other metallic survey markers, water or gas meters, conduit, and manholes. M-97 can sense manholes up to 42″ deep and valve boxes up to 18″ deep. Search coil is immersible in water. Operating frequency of search coil: 4.5 kHz. Sensitivity: 0.2mV RMS for full scale. Output indication: meter, 1 milliamp, 0-100 linear scale. Speaker, 16 ohm impedance. Headset, 8 ohm impedance. Audio frequency 450 kHz. Power supply: Two 9V batteries.