Counts revolutions of a Transform (around its +Z axis)

RevolutionCounter.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// @kurtdekker
//
//	Counts revolutions in degrees around the +Z axis of a transform
//
// NOTE: Like all things in a discrete digital simulation, this takes samples at
// regular intervals. This means rapid rotation of the transform will introduce
// more and more error term. Don't spin your transform rapidly if this is a concern.
//
// NOTE: Transform can be oriented however you like.
//	Rotation is alway measured around the local +Z axis
//
// To use:
//
//	- place this on a Transform that rotates around its +Z (such as a dial)
//	- read the total accumulated rotation out of TotalDegrees

public class RevolutionCounter : MonoBehaviour
{
	public float TotalDegrees;

	bool ready;		// to ensure we've been through once

	// last frame
	Vector3 previousForward;
	Vector3 previousRight;

	void Update ()
	{
		// this frame
		Vector3 forward = transform.forward;
		Vector3 right = transform.right;

		// ready or not, you haven't moved far enough that we can compute reliably.
		if ((right - previousRight).magnitude < 0.01f)
		{
			return;
		}

		if (ready)
		{
			// in case your steering axis is changing, we split the difference
			Vector3 axisOfRotation = (forward + previousForward) / 2;

			// this frame
			Vector3 arm1 = previousRight;

			// last frame
			Vector3 arm2 = right;

			// take out incidentals related to axisOfRotation changing
			arm1 = Vector3.ProjectOnPlane( arm1, axisOfRotation);
			arm2 = Vector3.ProjectOnPlane( arm2, axisOfRotation);

			Vector3 cross = Vector3.Cross( arm1, arm2);

			// and this is the portion of that cross vector lying along the axis of rotation
			float dot = Vector3.Dot( cross, axisOfRotation);

			// cross product builds magnitude like a sine curve
			float radians = Mathf.Asin( dot);

			float degrees = radians * Mathf.Rad2Deg;

			TotalDegrees += degrees;
		}

		// age the data
		previousForward = forward;
		previousRight = right;

		ready = true;	
	}
}