I’ve just read in the “Blender Manual” here that the values for X, Y and Z within the “Quaternion Rotations” define a “Rotation Axis” and W a “Rotation Angle” around that axis. But setting it to “Euler Rotations” can lead to a “Gimbal Lock”.
Rotate a bone in “Quaternion (WXYZ)” (default for bones in “Pose Mode”) around its “Local X Axis” and “W” as well as “X” will change!
