Now let's look at basic switch electrical functions, starting with contact rating. The principal switch ratings are volts AC or DC, current rating (milliamps or amps), electrical life (cycle at full power), contact resistance (measured in milliohms), and contact material (silver or gold). These ratings are necessary to properly match a switch type to a given application. Extremely low voltage and current typically requires the use of gold contact plating, while higher power contacts will require the use of alloyed silver contacts to minimize the probability of contact welding.