1. Wipe the blade clean and dry. Put the base on a flat, dry worktop.
2. Choose your angle: 15° for thin blades, 18° for small everyday knives, 20° for most kitchen knives, 22° for thick, heavy blades. Not sure? Start with 20°.
3. Pick your first disc: 240 grit for a very blunt or chipped edge, 400 grit for a blunt one, 1000 grit for a regular top-up. Fit it on the roller.
4. Rest the flat of the blade against the side of the base marked with your angle, edge facing up. The magnets hold it in place.
5. Hold the base still with one hand. Roll the disc back and forth along the edge, from heel to tip, with light pressure.
6. Turn the knife round and do the other side, at the same angle and with the same number of passes.
7. Move up one disc at a time, in grit order: 240, 400, 600, 1000, 5000, 8000. Do both sides with each disc.
8. Test the edge on a sheet of paper held upright. If it catches or tears, make a few more passes on each side with the last disc.
9. Wipe the blade clean before you cook with it, and wipe the discs with a dry cloth.
Keep your fingers on the roller and away from the edge while you roll.