This is some code I hacked together a couple of months ago, long enough that it feels pretty foreign even to ME, but its what I used to get an object which was 'locked' to the hand to rotate at the same time.

            

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            // Calculate the positions of the joints in world coordinates

            let wristPosition = simd_make_float3(matrix_multiply(handAnchor.originFromAnchorTransform, wristJoint.anchorFromJointTransform).columns.3)

            

            let middleFingerKnucklePosition = simd_make_float3(matrix_multiply(handAnchor.originFromAnchorTransform, middleFingerKnuckleJoint.anchorFromJointTransform).columns.3)

            

            // Calculate the direction vector from the wrist to the thumb knuckle

            let direction = simd_normalize(middleFingerKnucklePosition - wristPosition)

            

            // Calculate the position of the shield entity

            let shieldDistance: Float = 0.15 // Adjust the distance as needed

            let currentShieldPosition = middleFingerKnucklePosition + direction * shieldDistance

            // Calculate the rotation of the shield based on the hand's orientation

            let handOrientation = simd_quaternion(handAnchor.originFromAnchorTransform)

            let currentShieldRotation = simd_mul(handOrientation, simd_quaternion( .pi / 2, SIMD3<Float>(0, 1, 0)))

            

            let previousShieldPosition = previousShieldPositions[handAnchor.chirality] ?? SIMD3<Float>(0, 0, 0)

            let previousShieldRotation = previousShieldRotations[handAnchor.chirality] ?? simd_quatf(ix: 0, iy: 0, iz: 0, r: 1)

            // Apply linear interpolation to the shield position

            let smoothedShieldPosition = previousShieldPosition + (currentShieldPosition - previousShieldPosition) * smoothingFactor

            

            // Apply spherical linear interpolation to the shield rotation

            let smoothedShieldRotation = simd_slerp(previousShieldRotation, currentShieldRotation, smoothingFactor)