Metrication in the United States There are no U.S. customary units for electric current, potential difference, or charge since these concepts were developed after the international adoption of metric in science. The metric units ampere, volt, ohm and coulomb are the only units used. The SI term hertz has replaced the term "cycles per second" as a unit of frequency. Energy is often measured in watt hours, BTUs, therms or calories rather than the SI joule. Residential and commercial electrical energy use is metered and billed in kilowatt hours, kW·h, as in most metric countries. Force measurements regularly use the pound instead of the SI
Inch per second tape sound recording, magnetic tape speed is often quoted in inches per second (abbreviated "ips"). Also computer mice sensitivity is also often referred to in inches per second (abbreviated as "ips") along with g force. In rotorcraft health monitoring, rotor and shaft induced vibration levels are often quoted in inches per second. Inch per second The inch per second is a unit of speed or velocity. It expresses the distance in inches ("in") traveled or displaced, divided by time in seconds ("s", or "sec"). The equivalent SI unit is the metre per second. Abbreviations include in/s, in/sec, ips, and less