Fig. A1. (A) Pixel area resulting from stresses applied to the surface of gelatin by test tubes and flat-bottomed cylinders of different diameters (r²=0.11; N=44). (B) Pixel area as a function of force instead of stress for the data in A (r²=0.94; N=44). (C) Results of finite element model of calibration showing thresholded pixel area as a function of stress (500, 750 and 1000 Pa) for three different modeled radii (0.005, 0.010 and 0.015 m) (r²=0.16; N=9). (D) Pixel area as a function of force instead of stress for the data in C (r²=0.996; N=9).