C#

public partial class MainForm : Form
{
    public MainForm()
    {
        InitializeComponent();
    }

    private Thermometer _therm = new Thermometer();

    private void btnStartTempReading_Click(object sender, EventArgs e)
    {
        _therm.OnTempReading += new Thermometer.TemperatureHandler(ShowTemperatureMeasureMent);
        _therm.StartReading();
    }

    private void ShowTemperatureMeasureMent(Thermometer therm, ThermometerEventArgs e)
    {
        lblTemp.Text = e.Temperature.ToString("00.00");
        lblTime.Text = e.TimeOfMeasurement.ToString();
    }

    private void btnStopTempReading_Click(object sender, EventArgs e)
    {
        _therm.StopReading();
    }

class ThermometerEventArgs : EventArgs
{
    public double Temperature
    {
        get {
            Random rand = new Random();
            return (rand.NextDouble() * rand.Next(-50, 50));
            }
    }

    public DateTime TimeOfMeasurement
    {
        get { return DateTime.Now; }
    }
}


class Thermometer
{
    #region events and delegates
    public event TemperatureHandler OnTempReading;
    public delegate void TemperatureHandler(Thermometer therm, ThermometerEventArgs e);
    #endregion

    private System.Threading.Timer _timer;
    private Form _form;

    public void StartReading()
    {
        if ((OnTempReading != null) && (_timer == null))
        {
            _timer = new System.Threading.Timer(delegate(object o) { OnTempReading(this, new ThermometerEventArgs()); }, null, 5000, 5000);
        }
    }

    public void StopReading()
    {
        _timer.Dispose();
    }
}