The gun tester is used to verify that the following items on the gun work.
The two gun cables are plugged into the end of the tester.
The end of the gun is aligned with the front of the tester. The photodiode is placed over the LED.
When the trigger is pulled it will turn on the 'Shooting LED' and the 'Hit Inidicator LED'. If the gun photodiode is working the LED on the side of the tester will come on.