The magnetic moment is a quantity that describes the magnetic strength of an entire object. Sometimes, though, it is useful or necessary to know how much of the net magnetic moment of the object is produced by a particular portion of that magnet. Therefore, it is useful to define the magnetization field M as: M = m Δ Δ V V Δ Δ V , where m Δ V and V Δ V are the magnetic dipole moment and volume of a sufficiently small portion of the magnet Δ V. This equation is often represented using derivative notation such that M = d m d V , where d m is the elementary magnetic moment and d V is the volume element. The net magnetic moment of the magnet m therefore is m = ∭ ∭ M d V , where the triple integral denotes integration over the volume of the magnet. For uniform magnetization (where both the magnitude and the direction of M is the same for the entire magnet (such as a straight bar magnet) the last equation simplifies to: m = M V , where V is the volume of the bar magnet.