Comparison of force signals recorded during the Zwick/Roell testing machine validation test for the measuring device, including a time-resolved error measure. Top: Reference force measured by the Zwick/Roell ZwickiLine compression testing machine (red) and reconstructed forces from the mouthpiece measuring system (MS) for total force (black), upper-lip force (yellow), and lower-lip force (green). Grey shaded regions indicate quasi-static force plateaus detected from the reference signal. Bottom: Sliding-window relative root-mean-square error (rRMSE) between the total force recorded by the mouthpiece and the reference force, computed over a 0.2 s window, where the RMSE in each window is divided by the mean absolute reference force within the same window.