You can destroy metal-oxide semiconductor transistors and other electronic parts in an instant if you have static electricity on your hands or work area. Specially treated plastic mats, called electrostatic discharge, or ESD, mats, lay on top of your bench and safely remove static charges as you work. These mats drain static electricity without shorting out any electronics. Contamination and wear can increase a mat's resistance and compromise its performance, so you need to test the mats periodically to tell if they need cleaning or replacement.
Connect the mat's grounding clip to the electrical ground connection. You can use grounded metal conduit or a cold water pipe for an electrical ground.
Turn the mat test meter on. Clip one probe to the mat's metal snap or grounding point. Touch the other probe to the furthest point on the mat's surface away from the grounding point. A good mat will either light up the meter's "good" light or indicate a resistance of between 1 million and 10 billion ohms.
Move the 2-meter probes to opposite ends of the mat, touching the mat's surface. The meter should read a consistent resistance of more than 1 million ohms. Move the probes to a different point on the mat's edge, always keeping them at opposite sides. The meter should continue to show a resistance between 1 million and 10 billion ohms, or light its "good" light.
The high end of an ESD mat's resistance will be beyond the measuring range of a typical multimeter. A meter that can accurately measure into the gigohm, or billion ohm, range is best for testing these mats.