Left: Top view of the mouthpiece electronics showing the angular arrangement of the four load cells, with an 80° separation between the two sensors assigned to each lip. Right: Schematic of the axial force balance used for the equilibrium-based derivation of the upper- and lower-lip contact forces (F _UL, F _LL), indicating the summed load-cell reactions (F _1, 2, F _3, 4), their effective lever arms (l _1, 2, l _3, 4), the mouthpiece centre (O), and the rim diameter (D _m).