Portable electronic device for measuring a physical quantity, including at least one sensor device that measures and converts the value, or variation, of a physical quantity into an analog electrical signal and an electronic device, which acquires the analog electrical signal, converts it into digital format and calculates the engineering value in real time, comprising two distinct physical units operationally connected in a dismountable manner, of which: • the first of said physical units is a smart mobile electronic device; • and wherein the second of said physical units comprises said at least one electrical/electronic sensor device, a jack connector corresponding to said microphone connecting port on said first unit, and electrical/electronic means that convert said analog electrical signal, generated by said at least one sensor device, into a frequency value and transmit it to said output jack connector.