A handy Servo Tester.
A nice compact servo tester. It has 3 different modes - manual (use dial to adjust servo), servo center and auto sweep (runs servo back and forth), which comes in handy when testing your control surface geometry or breaking in a new servo.
We really like these little guys when we are breaking in a new servo, or anytime we are installing servos into a plane. A quick and easy way to find the servos centered location.