Timer going too fast

[asantavicca]

So after letting it run for an hour, the timer seemed to be about 4 minutes too fast (i.e. after letting it count down for an hour, it finished about 4 minutes too quickly).

I'm thinking it's in my _Tick method. I know there's an issue with the milliseconds, but I think there might be a bigger issue.

Here's the tick method and some other info....any idea what I'm doing wrong here?

this.timer1.Interval = 10;
this.timer1.Tick += new System.EventHandler(this.timer1_Tick);

private void timer1_Tick(object sender, EventArgs e)
        {
            // Verify if the time didn't pass.
            if ((minutes == 0) && (hours == 0) && (seconds == 0) && (millisec == 0))
            {
                // If the time is over, clear all settings and fields.
                // Also, show the message, notifying that the time is over.
                timer1.Enabled = false;
                //MessageBox.Show(textBox4.Text);
                button1.Enabled = false;
                button3.Enabled = false;
                button2.Enabled = true;
                textBox3.Clear();
                textBox2.Clear();
                textBox1.Enabled = true;
                textBox3.Enabled = true;
                textBox2.Enabled = true;
                textBox1.Enabled = true;
            }
            else
            {
                // Else continue counting.
                if (millisec < 1)
                {
                    millisec = 59;

                    if (seconds < 1)
                    {
                        seconds = 59;
                        if (minutes == 0)
                        {
                            minutes = 59;
                            if (hours != 0)
                                hours -= 1;

                        }
                        else
                        {
                            minutes -= 1;
                        }
                    }
                    else
                        seconds -= 1;
                }
                else
                    millisec -= 1;
                // Display the current values of hours, minutes and seconds in
                // the corresponding fields.
                char pad = '0';
                currentTime.Text = hours.ToString().PadLeft(2, pad)
                    + " : " + minutes.ToString().PadLeft(2, pad)
                    + " : " + seconds.ToString().PadLeft(2, pad)
                    + " . " + millisec.ToString().PadLeft(2, pad);

            }
        }