1. A magnetic sensor system suitable for sensing local variations in an ambient magnetic field caused by a mass of ferromagnetic

material, the sensor system comprising:

a magnetic sensor assembly, including;

a first scalar point-sensor magnetometer, the first scalar point-sensor magnetometer having a first scalar magnetometer axis;

a second scalar point-sensor magnetometer, the second scalar point-sensor magnetometer having a second scalar magnetometer

axis;

a third scalar point-sensor magnetometer, the third scalar point-sensor magnetometer having a third scalar magnetometer axis;

the first scalar point-sensor magnetometer, the second scalar point-sensor magnetometer, and the third scalar point-sensor

magnetometer being fixedly mounted with respect to one another such that (i) the position of each of the scalar magnetometer

axes is invariable with respect to the other scalar magnetometer axes, and (ii) when the magnetic sensor assembly is in operation,

at any particular point in time,

the first scalar magnetometer axis forms a first angle with magnetic field lines of the ambient magnetic field at a location

of the magnetic sensor assembly in a first plane defined by the first scalar magnetometer axis and the magnetic field lines,

the second scalar magnetometer axis forms a second angle with the magnetic field lines of the ambient magnetic field at the

location of the magnetic sensor assembly in a second plane defined by the second scalar magnetometer axis and the magnetic

field lines,

the third scalar magnetometer axis forms a third angle with the magnetic field lines of the ambient magnetic field at the

location of the magnetic sensor assembly in a third plane defined by the third scalar magnetometer axis and the magnetic field

lines,

the first scalar magnetometer axis intersects a plane parallel to both the second scalar magnetometer axis and the third scalar

magnetometer axis at a fourth angle,

the second scalar magnetometer axis intersects a plane parallel to both the first scalar magnetometer axis and the third scalar

magnetometer axis at a fifth angle, and

the third scalar magnetometer axis intersects a plane parallel to both the first scalar magnetometer axis and the second scalar

magnetometer axis at a sixth angle; and

the first scalar point-sensor magnetometer having a first scalar magnetometer operating range defined with respect to a range

of values of the first angle, the second scalar point-sensor magnetometer having a second scalar magnetometer operating range

defined with respect to a range of values of the second angle, the third scalar point-sensor magnetometer having a third scalar

magnetometer operating range defined with respect to a range of values of the third angle;

the first scalar point-sensor magnetometer, the second scalar point-sensor magnetometer, and the third scalar point-sensor

magnetometer positioned with respect to one another such that, at the particular point in time, at least one of: the first

angle is within the first scalar magnetometer operating range, the second angle is within the second scalar magnetometer operating

range, and the third angle is within the third scalar magnetometer operating range; and

a non-transient computer-readable information storage medium storing program instructions that when executed by a computer

processor determine which of a first output from the first scalar point-sensor magnetometer, a second output from the second

scalar point-sensor magnetometer, and a third output from a third scalar point-sensor magnetometer is to be used at the particular

point in time in the sensing of local variations in the ambient magnetic field.