Question Use quaternion to determine rotation direction - Leap motion controller

Hey guys i am trying to use quaternion data (specifically Quaternion Bone Rotation) from leap motion controller to determine if the user is rotating their hand to the left or right.
I want the user to lift their hand up where all fingers face the -Y axis and rotate their hand along the Y-axis; i should get a change in yaw angle so that positive values indicate a left turn (counterclockwise) while negative values indicate a right turn (clockwise)

However, I encountered an issue: the delta yaw angles are very small: eg 0.001986674, 0.009016895, and -0.003356934 and they fluctuate a lot.
Here is my code:

Code (CSharp):

1.  Bone _indexMetacarpal = _index.Bone(Bone.BoneType.TYPE_METACARPAL);
2.                     Quaternion boneRotation = _indexMetacarpal.Rotation;
3.                     Vector3 currentEulerAngle = boneRotation.eulerAngles;
4.                     Vector3 deltaEulerAngle = currentEulerAngle - previousBoneRotation.eulerAngles;
5.                     if (deltaEulerAngle.y > 0)
6.                     {
7.                         Debug.Log("LEFT");
8.                     }
9.                     else if(deltaEulerAngle.y < 0)
10.                     {
11.                         Debug.Log("RIGHT");
12.                     }
13.  
14.                     previousBoneRotation = boneRotation;

What went wrong here? Should i use deltaEulerAngle.z instead of y because of how the hand is positioned?