对于 C# Stopwatch ElapsedTick 的疑惑

Question

A*算法的部分代码

    MLOG.time("newCostDealer");
    MLOG.time("newCostDealer - newCost");
    float newCost = cost_so_far[cur]+ heuristic(next.Pos, end.Pos);
    MLOG.timeEnd("newCostDealer - newCost");

    MLOG.time("newCostDealer - 0");
    bool tmp2 = !cost_so_far.ContainsKey(next);
    MLOG.timeEnd("newCostDealer - 0");

    MLOG.time("newCostDealer - temp3");
    bool tmp3 = false;
    if (!tmp2) {
        tmp3 = newCost < cost_so_far[next];
    }
    MLOG.timeEnd("newCostDealer - temp3");

    if (tmp2 || tmp3)
    {
        MLOG.time("newCostDealer - 1");
        frontier.put(next, newCost);
        MLOG.timeEnd("newCostDealer - 1");

        MLOG.time("newCostDealer - 2");
        cost_so_far[next] = newCost;
        // MLOG.info("came_from[next] = cur," + next.ToString() + " " + cur.ToString());
        came_from[next] = cur;
        MLOG.timeEnd("newCostDealer - 2");
    }

    MLOG.timeEnd("newCostDealer");

运行结果：

求教，为啥 newCostDealer ticks 和其它记录加起来差那么多丫？！

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使用的记录方法

    static public void time (string key) {
        if (timeKeyHub.ContainsKey (key)) {
            Debug.LogError ("MLOG.cs time key already exist");
        } else {
            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch ();
            timeKeyHub.Add (key, sw);
            sw.Start ();
        }
    }
    static public void timeEnd (string key) {
        if (timeKeyHub.ContainsKey (key)) {
            System.Diagnostics.Stopwatch sw;
            timeKeyHub.TryGetValue (key, out sw);
            sw.Stop();
            Debug.Log (string.Format ("<color=blue>{0}</color> {1} ms {2} ticks", key, sw.ElapsedMilliseconds, sw.ElapsedTicks));
            // BIRDTODO:用池子
            sw = null;
            timeKeyHub.Remove (key);
        } else {
            Debug.LogError ("MLOG.cs timeend key not exist");
        }
    }