you can use simple winforms timers to update textbox's content

Code:
                int ms = 1000;
                System.Windows.Forms.Timer expTimer = new System.Windows.Forms.Timer();
                
                expTimer.Interval = ms;
                expTimer.Tick += (sender, e) => { expTextBox.Text = ReadExp().ToString(); };
                expTimer.Start();
supposing you have an expTextBox and a ReadExp function, ofc.

You may get confused with line "expTimer.Tick += (SENDER, E) => ...", this is because I'm lazy and do not like to write something like:

Code:
expTimer.Tick += new System.EventHandler(expTimer_Tick);
and somewhere write:
Code:
void expTimer_Tick(object sender, EventArgs e)
{
      expTextBox.Text = ReadExp().ToString();
}