A Hall-Effect sensor is a transducer that varies its output voltage in response to changes in magnetic field strength. Hall sensors are often used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analog transducer producing a linear output voltage directly proportional to the magnetic field strength. With a known magnetic field, its distance from the Hall plate can be determined. Using groups of sensors, the relative position of the magnet can be deduced. Movement of electric charge through a conductor will produce a magnetic field that varies with current, and a Hall sensor can be used to measure the current without interrupting the circuit. Typically, the sensor is integrated with a wound core or permanent magnet that surrounds the conductor to be measured. Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital (on/off) mode, and may be called a switch. Hall-effect sensors are commonly seen in industrial applications and are also often used in consumer equipment. A magnetoresistive digital sensor is a magnetic sensor that operates very much like a Hall effect.  However, magnetoresistance is roughly 100 times more sensitive than the Hall-effect. Another advantage of MR sensors in applications that count revolutions is that the resolution is effectively doubled, as MR sensors are omnipolar (operates with North or South pole). Hall-effect sensors respond to fields perpendicular to the sensor while MR sensors respond to parallel fields. A Hall-effect vane sensor is a digital output sensor consisting of a magnet and Hall-effect transducer fixed in a rigid package. The sensor has a gap through which a ferrous vane may pass. The Hall-effect transducer is designed to detect the presence or absence of the vane. Another sensor variation is the gear tooth sensor based around a Hall-effect transducer that is packaged into a cylindrical housing. When a ferrous material passes by the sensing face, the gear tooth sensor is designed to detect the presence or absence of this material.