Print this calibration tool and create little swatches you can go back to and read off the volume (in mm cubed) of material needed to purge a given color change.
All 5 colors swap with all 4 of the other colors in each direction. That's 20 color changes total. To reduce the number of color changes (eg to calibrate for 3 filaments only) you can go into the 3mf file and delete the color changes that are not needed.
The author remixed this model.