Fig. 4

Gyro performance of displacement measurement between our device and commercial product (comm. gyro). a Angular velocity signals (with 15Hz low-pass filtering) during four slow and four fast stretches. The signals were almost identical with very good correlation (CC = 0.9957). b The derived displacement signals both showed a drift phenomenon (an upward trend was noted). The green arrows indicated the start position of each stretch and were used as a reference to calculate each stretch displacement. c For all stretch cycles, the displacement from our gyro was very close to the commercial gyro with a maximal error percentage of 1.7 %