The ammeter bases its operation on the Biot-Savart law according to which a magnetic field is produced around a conductor that carries an electric current. If we know the value of the field we could calculate the current in the conductor.
The user must locate the magnetic sensor of the cell phone, which is usually at the top. Then bring the cable or phase line closer to the phone. The measurement is better without the phone case as it reduces the field measurement, however we can increase the calibration constant and verify the measurement with a clamp ammeter or using a reference value. Once the user modifies the calibration, its value will continue to be used in subsequent measurements.
The application has the functionality of a clamp ammeter with the advantage that the measurement can be made directly with the electrical cord of the appliance and does not require separating the phase line