A threshold voltage distribution of a set of storage elements in a memory device is measured by sweeping a control gate voltage while measuring a characteristic of the set of storage elements as a whole. In the sensor device, an ADC outputs, to one of two input terminals of a comparison circuit, second data which is a digital value ADCOUT corresponding to a current Iin\u2212I1 being the result of subtraction from a current I1 from a current Iin and which is larger than a threshold Data_th. a sealing coat, joint coat andor joint pointing coat, which joints adjacent said prefabricated elements to form a substantially plane outer surface. This can take the form of identifying each specific app on the mobile device that has an unreleased wake lock at any point during the given period of time while the screen is off. In one embodiment the extracted features include color and textual features.