The Triplett USB-Bug is designed to test the power, voltage, and current of USB 2. or USB 3. charging ports. Connect the USB-Bug inline between the power source and the device you are trying to charge. Test current from to 3 Amps. If the current is over 3 Amps, the USB-Bug will flash the decimal point quickly. Test voltage from 3.2 VDC to 3 VDC. If the voltage is greater than or equal to 5.6 VDC, the decimal point indicator on the voltage measurement will flash quickly. If the voltage is less than 4.4 VDC, the decimal point indicator on the voltage measurement will flash slowly. Test power from to 99.9W. Test Capacity: the USB-Bug will display the Amp hours (Ah) and milliamp hours (mAh) that have passed through the Tester. This displays as a cumulative number and is useful when determining how quickly/effectively a portable battery charger is working. The USB Bug has a built-in Smart Chip for Intelligent Charging that allows it to determine the safest maximum current your PD can accept. It can charge your phone or tablet up to 5% faster than aftermarket/generic chargers. There are two USB out ports. The top port, called the Unmasked Port, allows data to transfer while charging. The bottom port, called the Masked Port, blocks any data from being transferred. You can use the Masked Port to charge your phone or tablet without having to worry about anyone accessing your data.