Plain English Meaning

When the datum (the zero point used for weight and balance) sits behind something on the aircraft, that item's distance from the datum is written as a negative number. Anything forward of the datum gets a minus sign so the math works out correctly.

Full Definition

In weight and balance calculations, an arm (the horizontal distance from the reference datum to the center of gravity of an item) that lies forward of the datum, expressed as a negative number. When multiplied by the item's weight, it produces a negative moment, which is subtracted from the total moment when computing the aircraft's center of gravity.

Context Anchor

Seen in weight-and-balance calculations when an aircraft has equipment, fuel, baggage, or another item located forward of the reference datum.