An invasive medical device for insertion into a patient, the device comprising: a hypodermic needle having an elongate shaft having an outer diameter "D", an outer surface 228, a distal tip, and a proximal end, the diameter of the elongate shaft sized to be inserted within an intravenous catheter, at least a portion of the elongate shaft having a first magnetic region having a first length located at a fixed distance from the distal tip in the first magnetic region, intravenous catheter tubing, wherein the elongate shaft is disposed within the intravenous catheter tubing, a needle subassembly further including a needle hub mounted to the proximal end of the needle, and the intravenous catheter tubing is part of a catheter adapter subassembly characterized in that: the first magnetic region includes a discontinuity (235, 335), the discontinuity (235, 335) selected from the group consisting of an electroless plated layer of ferromagnetic metal at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, an electroplated layer of ferromagnetic material at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, a layer of paramagnetic metal at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, a spot weld of magnetic metal at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, and a magnetic adhesive at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, and the discontinuity is placed at a known location at a fixed distance from the distal tip such that first magnetic field of the first magnetic region is detectable by an array of magnetometers to provide a position of the first magnetic region based upon the magnetic field strength of the first magnetic region, and the catheter adapter subassembly further comprises a magnetic feature having north and south poles on axis with the catheter tubing and the needle and a known geometrical relationship to one or more features fixed on the catheter assembly to provide a measurement datum that is measureable by the array of magnetometers (672, 673, 674). a hypodermic needle having an elongate shaft having an outer diameter "D", an outer surface 228, a distal tip, and a proximal end, the diameter of the elongate shaft sized to be inserted within an intravenous catheter, at least a portion of the elongate shaft having a first magnetic region having a first length located at a fixed distance from the distal tip in the first magnetic region, intravenous catheter tubing, wherein the elongate shaft is disposed within the intravenous catheter tubing, a needle subassembly further including a needle hub mounted to the proximal end of the needle, and the intravenous catheter tubing is part of a catheter adapter subassembly characterized in that: the first magnetic region includes a discontinuity (235, 335), the discontinuity (235, 335) selected from the group consisting of an electroless plated layer of ferromagnetic metal at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, an electroplated layer of ferromagnetic material at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, a layer of paramagnetic metal at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, a spot weld of magnetic metal at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, and a magnetic adhesive at which the outer diameter of the needle at the discontinuity is larger than the outer diameter "D" at the remainder of the needle, and the discontinuity is placed at a known location at a fixed distance from the distal tip such that first magnetic field of the first magnetic region is detectable by an array of magnetometers to provide a position of the first magnetic region based upon the magnetic field strength of the first magnetic region, and the catheter adapter subassembly further comprises a magnetic feature having north and south poles on axis with the catheter tubing and the needle and a known geometrical relationship to one or more features fixed on the catheter assembly to provide a measurement datum that is measureable by the array of magnetometers (672, 673, 674).