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 50% 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.