ゲーム内時間の経過時間を求めるタイマー

Timer.cs

using UnityEngine;
using System.Collections;

public class Timer : MonoBehaviour
{
  private float startTime;

	public float second = 0;

	void OnGUI ()
	{
		if (GUILayout.Button ("Reset)) {
			startTime = Time.time;
		}

		if (startTime != 0) {
			second = (Time.time - startTime);
		}
		GUILayout.Label (second.ToString ());
	}
}