We are routinely asked, “what tests should I perform on my transformers?” and the answer is, it depends. Why are you testing? How old is the apparatus? What is its history? Do you even have historical data? If so, any trends? Has the apparatus experienced any faults recently? In the past? No one test will tell you everything you need to know about your apparatus, and for a variety of reasons you aren’t always perform every test available. Understanding what each test each test can tell you, but also how results can be used to confirm the data of other tests, will help you to make that decision.