It is a series resistor inside capacitor, using 100kHz to remove the impedance 1/(2*pi*F*C). The impedance become small, and then measure the true series resistor value. Using this , measure the capacitor is / damaged or good in condition. Our ESR meter only applies less than 15mV DC or to on a good capacitor, as a result use it as in circuit test. During repairing TV, LCD, Audio board, etc. in circuit testing the capacitor is good or not. This MESR-100 auto-ranging capacitor ESR and low Ohm meter measuring range from 0.001 to 100.0R, support in circuit testing. Using true 100 KHz sine wave to measure the ESR value, which is equal to the testing of capacitor manufacturer. Dual terminal, for fast and easy inspect internal resistance of the capacitor, a ESR table for fast check. Note: The Capacitance Meter is used for testing the internal resistance of the capacitor, not for testing capacitance value. Accuracy: Up to 1% Wide Measurement Range: 1uF High Resolution: 4 digit, or 0.001Ohm @ 1 range Measuring voltage: Less than ~40mV RMS (TESTING VOLTAGE) External Power: 5V -USB Operating Current: 0.02A Battery: 2 * AA 1.5V Battery (not included) Battery Life time: 80 Hours Note: Shipment not included batteries Colour:black+yellow Material:plastic Package Contents: 1 x Capacitance Meter with SMD Test Clip Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.