The Megger PAT450 is a portable appliance tester that is used to test the safety of electrical appliances. It is a compact and lightweight tester that is easy to use, making it ideal for testing appliances in a variety of settings. The PAT450 can perform a range of tests, including insulation resistance, earth continuity, and polarity. It also has a built-in memory that can store up to 1000 test results.