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For the same geometry, field strength and induced magnetization model at the opposite magnetic inclination, replacing $I$ by $-I$ gives $\Delta T_{-I}(x)=\Delta T_I(-x)$. Thus the north–south asymmetry reverses: the principal low moves to the northern side and the high to the southern side. It is a horizontal reflection of the simple profile, rather than a necessary reversal of every anomaly's sign. At a magnetic pole the induced anomaly is symmetric; at the magnetic equator the symmetry is different again. If remanent magnetization dominates, a hemisphere change alone does not determine the new profile because that remanence direction also has to be specified.

Assume that the intrusion has a positive magnetic susceptibility contrast, that induced magnetization dominates its remanent magnetization, and that the local present-day geomagnetic field points roughly northward and downward, as in this northern mid-latitude setting. Writewhere $\mathbf{b}$ is the anomalous magnetic field and the last expression assumes $|\mathbf{b}|\ll |{\mathbf{B}}_0|$. A total-field magnetic anomaly measures a field projection, so it need not have the same sign everywhere above a high-susceptibility body.^[ref]

The 100 km east–west extent makes an approximately two-dimensional, east–west-striking body a useful model away from its ends. On a profile drawn north on the left, south on the right, the expected normally induced response has a subsidiary negative lobe on the northern side and a stronger positive lobe over the body, displaced towards the south. The northward horizontal field component makes the anomaly asymmetric; its downward component produces the dominant positive response. The field falls back towards the regional value away from the intrusion. Broad bodies can have edge shoulders or a broad central high, so the sketch represents a qualitative shape rather than one uniquely specified curve.

An exactly vertical inducing field would remove this north–south skew for a symmetric induced body. Real magnetic inclination and magnetic declination should be taken from a suitable geomagnetic field model for the survey date and location; no exact local value is supplied here. Strong oblique or reversed remanent magnetization can shift or reverse the lobes, and heterogeneous magnetic susceptibility, body dip and three-dimensional end effects can alter the profile. Higher magnetic susceptibility alone does not determine a unique amplitude or polarity pattern without these qualifications.

Strong geological magnetic anomalies generally occur in rocks containing abundant strongly magnetic iron oxides, especially magnetite and titanomagnetite. Many mafic rocks, including basalt and gabbro, and some ultramafic rocks have large signatures; magnetite-rich iron formations can be exceptionally strong, while serpentinization can create additional magnetite. Actual magnetic susceptibility and remanent magnetization, rather than the rock name alone, determine the response. Sedimentary and felsic rocks are often weaker but have important exceptions.

Magnetite, titanomagnetite and maghemite exhibit strong ferrimagnetism; some pyrrhotite is also strongly magnetic. Hematite is generally much weaker in induced magnetic susceptibility, although it can carry stable remanent magnetization. Quartz and calcite have very small, usually negative, susceptibilities, and many ordinary silicates have only weak paramagnetism. A steel car exhibits strong ferromagnetism and can therefore stand out against a weakly magnetic host, but its shape and pre-existing remanent magnetization complicate the signal.^[ref]

The sketches assume the car can be approximated by a compact magnetic dipole whose induced magnetic moment is parallel to the local geomagnetic field. The host contributes negligible local contrast. Real steel also has remanent magnetization and shape-dependent magnetization, so the car's actual profile need not follow this idealization. A proton-precession magnetometer observeswhen $|\mathbf{b}|\ll |{\mathbf{B}}_0|$. This scalar total-field magnetic anomaly must not be confused with a fixed vertical field component. For induced $\mathbf{m}=m{\hat{\mathbf{B}}}_0$, the magnetic dipole field givesReversing both the inducing field and induced moment leaves this total-field magnetic anomaly unchanged, exactly for the magnitude definition as well as in the weak-anomaly approximation.^[ref]

Near the south magnetic pole, the inducing magnetic field and induced magnetic moment are vertically upward. Directly over the car its dipole field is also upward, again reinforcing the main field. The total-field magnetic anomaly is therefore the same positive central high and weak negative side lobes as at the north magnetic pole under the same induced-dipole assumptions. A fixed signed vertical field component would reverse, but the scalar field strength measured by the proton-precession magnetometer does not. If the car's remanent magnetization dominates, neither this symmetry nor these predicted signs is assured.

A planetary magnetic field may include an intrinsic field maintained by an internal planetary dynamo, local crustal remanent magnetization, and externally driven fields associated with the solar wind. Separating these components requires spatial and temporal observations. A global internally sourced field, a localized crustal anomaly, and an induced magnetosphere are different evidence about the planet's present and past interior.

Acquisition of a younger remanent magnetization that partly or completely replaces an older magnetic record. Heating, chemical alteration or later mineral growth can cause it. A successful continental reconstruction must connect the age of the measured magnetic component to the geological event being reconstructed.

Remanent magnetization is magnetization retained after the applied magnetic field has been removed. Magnetic minerals cooling in an ambient field can preserve information about that field in a planetary crust. Such a record may outlive the planetary dynamo which originally produced it. Crustal remanence therefore differs from a present field maintained by conducting-fluid motion.