If ____ is set on the altimeter subscale, the altimeter will display ZERO when on the ground.

QFE is the altimeter setting that causes the altimeter to read zero when the aircraft is on the ground at the reference airport. This setting is commonly used for circuit training and precision approaches where height above the airfield is the critical reference. QNH shows altitude above mean sea level, and QNE is the standard altimeter setting of 1013.25 hPa used at higher altitudes.