Flight Level
In the United States, pilots flying above 18,000 feet (5,486 meters) are required to set the digits in the altimeter's Kollsman window to 29.92. The resulting altimeter reading is called a flight level. When the Kollsman window is set to 29.92 (1013.2 millibars) and the altimeter reads 30,000 feet, the altitude is stated as, "Flight Level 300 (three zero zero)."