Fig. 4. Accuracy, repeatability and hysteresis analysis. a, Displacement error through 2,700 node instances samples collected from 300 frames. b, The corresponding room-mean-square error of each tracked node displacement. c, Error distribution compared with the distance from the fixed point (A7) and the node displacement. d, Setup for hysteresis and repeatability tests. The short edge of the shape sensor is clamped, with a linear actuator lifting the distal edge vertically. e, Hysteresis plot of three FBGs AB and C under bending cycles (0.5 Hz), by fitting curves through sampling points. f, Peak displacement of the three sides, i.e., the clamped side (red), the middle line (cyan), and the distal side (green). The sensor showed high repeatability during 1,000 bending cycles. Quantitative comparison of the displacement fluctuation on a logarithmic scale (right).