Magnetic Index Positioner

A method comprising:

• mounting a second mandrel to a first mandrel;
• moving the first mandrel longitudinally relative to the second mandrel to cause a first-part magnetic element to disengage from a first of a plurality of second-part magnetic elements;
• and
• moving the first mandrel longitudinally relative to the second mandrel to cause the first-part magnetic element to engage a second of the plurality of second-part magnetic elements.

A system comprising:

• a first mandrel;
• a second mandrel mounted to the first mandrel and moveable longitudinally relative to the first mandrel among a plurality of index positions;
• a first-part magnetic element coupled to the second mandrel;
• and
• a plurality of second-part magnetic elements coupled to the first mandrel at respective positions, such that:
• the first-part magnetic element is adjacent to a respective one of the plurality of second-part magnetic elements when the second mandrel is at a respective index position, and
• a threshold force F on the second mandrel applied for a threshold time T is required to displace the first-part magnetic element from the respective second-part magnetic element sufficiently that the first-part magnetic element will not return to be adjacent to the respective second-part magnetic element when the force F is removed;
• and
• an electromagnetic intervention that adjusts the force F by interacting with a magnetic field of a permanent magnet.