ゲーム外時間の経過を求めるタイマー

Timer.cs

using UnityEngine;
using System.Collections;
 
public class Timer : MonoBehaviour
{
	private float startTime;
	public float second = 0;
 
	void OnGUI ()
	{
		if (GUILayout.Button ("push")) {
			startTime = Time.realtimeSinceStartup;
		}
 
		if (startTime != 0) {
			second = (Time.realtimeSinceStartup - startTime);
		}
		GUILayout.Label (second.ToString ());
	}
}