Here’s one way to look at it, according to Professor Van Hecke:

1. Heat the cocoa butter to liquid above 37 deg C (on the phase diagram, pass up through all 6 phases)
2. Cool it quickly to below 33 deg C so that crystal VI doesn’t have the time to form (on the phase diagram pass quickly through the crystal VI-liquid zone to the crystal V zone).
3. Hold the butter at say 30 deg C (above 27 so that crystal IV can’t form). Hold it long enough to convert as much as you can to crystal V solid.
4. Then cool quickly to room temperature (pass through the crystal I, II, III, and IV zones). It should all be solid, so the crystal-phase transitions should be inhibited.

This holding at a temperature below the crystal-V-forms temperature but above the crystal-IV-forms temperature is called “tempering” and maximizes formation of crystal V by not allowing crystal VI time to form.