The Fluke PRV240FS Proving Unit with FieldSense Technology provides a fast, safe and reliable sourcing method to verify that your electrical test tool is operating properly before you conduct any live tests - all without having to make electrical contact. The concept of "Test Before Touch" (TBT) involves testing your test tool against a known live source before and after the actual measurement. This sequence verifies that your test tool is operating properly during the actual measurement.