Regarding a solenoid and a sensor...Was the axial reading different from the reading in the middle of the coil when the sensor was inside but by ends?
It would probably be consistent from end to middle, to the other end. A solenoid is a tightly wound helix of electrical wire, usually wrapped around a ferromagnetic core. When an electrical current is conducted through the wire helix, an induced electromagnetic field is produced. This is the governing principle in electromagnets. Depending on the strength of the current fed through the electrical wire, the magnetic field may be large or small. The magnetic field that is produced would be consistent for the length of the wire helix, it would not fluctuate and have different readings by the sensor. It would produce the same reading across the board, whether by the ends, or in the middle. Induced electromagnetic fields have lots of application, from being put to use in the recycling industry, to producing maglev trains capable of speeds in excess of 300 miles per hour.