C#ProgressBar出现意外步骤

我有一个ProgressBar和一个Timer。

我想显示1小时的进度：每秒增加1/3600。

当我运行应用程序时，30分钟后，进度条的进度约为100%。我预计30分钟后会达到50%为什么？

    public Form1()
    {
        InitializeComponent();
        this.timer1.Tick += new EventHandler(timer1_Tick);
        this.timer1.Interval = 1000;
        this.timer1.Start();
    }
    private void timer1_Tick(object sender, EventArgs e)
    {
        this.progressBar1.PerformStep();
    }

-

        // 
        // progressBar1
        // 
        this.progressBar1.Location = new System.Drawing.Point(12, 29);
        this.progressBar1.MarqueeAnimationSpeed = 1000;
        this.progressBar1.Maximum = 3600;
        this.progressBar1.Name = "progressBar1";
        this.progressBar1.Size = new System.Drawing.Size(100, 23);
        this.progressBar1.Step = 1;
        this.progressBar1.TabIndex = 2;