You have just come from your annual physical checkup. The doctor has ordered a blood test, and a few of the results have come back out of the normal range. He scheduled you for a few more diagnostic tests such as x-ray, treadmill, and EKG. Those test results are inconclusive. Further tests are required to provide a complete diagnosis. Due to advances in the medical field, tests such as CAT scan and MRI are available. In the power industry there are advanced tests available for transformers when the blood test result (oil test) comes back out of the normal range. In the past, you could do a power-factor test, turns-ratio test, and a winding-resistance test to try to diagnose a problem in the transformer. There are new tests available to the power industry where more complete diagnosis can be performed.