IMU	Inertial Measurement Unit
DOF	Degree of freedom
FQA	Factored quaternion algorithm
GDA	Orientation estimating algorithm using a gradient descent algorithm
CF	Complementary filter proposed by this paper
KF	Kalman filter improved by this paper
FCF	A fast complementary filter whose fusion coefficients should be pre-tuned manually
GN	An improved algorithm using Gauss-Newton method