The GT Power Professional Digital Servo Tester is our top-of-the-line servo tester. This professional series servo tester has several function modes (see below) for the most comprehensive diagnostic of your servos. Why do you need a servo tester? - Bad servos can keep your grounded or can lead to costly, devastating crash. This portable device allows you to test the functionality of your servos and ESC without having to connect your radio, receiver and battery. Servos testers also allow you to easily center your servos when attaching servo horns and making control surface adjustments. This time-saving tool is a must have tool for any RC enthusiast.