°—degrees.

ASTM—American Society for Testing and Materials.

ATV—all-terrain vehicle.

cc—cubic centimeters.

CFR—Code of Federal Regulations.

CH₄ methane.

cm—centimeter.

C—Celsius.

CO—carbon monoxide.

CO₂—carbon dioxide.

EPA—Environmental Protection Agency.

F—Fahrenheit.

g—grams.

g/gal/day—grams per gallon per test day.

g/m /day—grams per meter-square per test day.

HC—hydrocarbon.

Hg—mercury.

hr—hours.

km—kilometer.

kW—kilowatt.

LPG—liquefied petroleum gas.

m—meters.

mm—millimeters.

mW—milliwatts.

N₂O nitrous oxide.

NARA—National Archives and Records Administration.

NMHC—nonmethane hydrocarbons.

NO_X—oxides of nitrogen (NO and NO_X).

psig—pounds per square inches of gauge pressure.

rpm—revolutions per minute.

SAE—Society of Automotive Engineers.

SI—spark-ignition.

THC—total hydrocarbon.

THCE—total hydrocarbon equivalent.

U.S.C.—United States Code.