For starters, your outlet tester has six scenarios. You can come across and from top to bottom. They read open, ground, open, neutral, open, hot, hot, and ground, reversed, hot, neutral, reversed, and correct. The little dots to the right represent the order in which the lights will come on. Representing each individual scenario, any scenario you come across with the exception of correct will need to be addressed by a qualified electrician. Here's an example of the outlet tester being used in four scenarios. Scenario number two is the only one that's correct. An outlet in properly working order should have 120 volts plus or minus 10%. The trick to this is that the lights on the tester don't require 120 volts. To illuminate, a technician must verify the proper voltage at an outlet regardless of its working or non-working condition. This process must be done using a multimeter in which the technicians should read 120 between hot and neutral, 120 between hot and ground, and zero between neutral and ground.