Boxplots of the normalised force ratio for notes from the easier section, ordered by proficiency level (left: beginners; right: professionals). Box shading encodes variability as the interquartile range (IQR), with darker shading indicating greater variability across notes. The four dark-red boxes highlight the participants with the highest interquartile ranges. The two dark-red vertical lines mark the boundaries between the theoretical proficiency groups (beginners, advanced, and professional musicians).