n. The angle between the leading edge of the flame and the horizon with origin at the base of the flame’s leading edge.
Flame angle is referenced to the leading edge mainly because it then follows the streamlines in the flame. Flame angle has also been defined alternatively as the cord angle from the tip of the flame to a point along the base of the flame midway between the leading and trailing edge.
Regardless of which definition is followed, it is critical to specify which definition is being used in relation to data that have been collected; likewise, it is also critical to verify which definition is being used in relation to data received from others. See Anderson and others (2006) for further discussion.