Thinking about springs to apply downforce on plotting pen holders suggested magnets, so I extricated some neodymium bars from my collection of power toothbrush heads:
![Magnets - single](https://softsolder.com/wp-content/uploads/2018/04/img_20180405_131136-magnets-single.jpg?w=749&h=562)
A snippet of magnetic field visualization film shows a dipole pattern:
![Magnets - single - field visualization](https://softsolder.com/wp-content/uploads/2018/04/img_20180405_131130-magnets-single-field-visualization.jpg?w=749&h=562)
Snapping two of them together in line:
![Magnets - in line](https://softsolder.com/wp-content/uploads/2018/04/img_20180419_200638-magnets-in-line.jpg?w=749&h=562)
… produces a quadrupole:
![Magnets - in line - field visualization](https://softsolder.com/wp-content/uploads/2018/04/img_20180405_131237-magnets-in-line-field-visualization.jpg?w=749&h=562)
Now, if only I had some magnetic monopoles, this whole thing would be easier!