You can use the universal USB 5V interface power supply, can also use an external DC power supply or 9V battery. The number of components is small, all straight-line components, installation and commissioning simple. Addition and subtraction frequency for the measurement of radio transceivers and other equipment. You can select the power saving mode, if the frequency is not obvious changes within 15 seconds automatically turn off the display. Measurable frequency range 1 Hz -50 MHz. Can measure the oscillation frequency of most commonly used crystal. The crystal oscillator of 32.768KHZ cannot be measured. Only the crystal oscillator of 4-20MHZ can be measured under limited conditions, and the crystal oscillator of 48MHZ can also be measured. However, because this crystal oscillator uses 3 harmonics, the measurement of the 48MHZ crystal oscillator will display the fundamental frequency of 16MHZ. ,As shown : You can also directly input the frequency signal between IN and G (ground) for measurement, and pay attention that the amplitude of the measurement signal should not be higher than 5V to avoid damage to the IC. The following picture shows the display of input 1HZ and 10KHZ: All in-line components can be soldered correctly according to the PCB silk screen. After soldering, use the standard signal source to input the signal, and adjust the yellow adjustable capacitor to make the displayed value to the signal frequency. You can use signal generator to adjust, if there is no standard signal, you can also use a crystal oscillator with better accuracy for direct calibration. The power supply can use a USB to 3.5mm power cable, or directly input 5-9V DC power supply at the - and + pads. colour: red Material: PVC Size: 10x5x5cm Package Contents: 1 x frequency meter(requiresassembly) Only the above package content, other products are not included. Note: Light 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.