C#

// The following method demonstrates overriding the
// caching policy for a request.
public static WebResponse GetResponseNoCache(Uri uri)
{
    // Set a default policy level for the "http:" and "https" schemes.
    HttpRequestCachePolicy policy = new HttpRequestCachePolicy(HttpRequestCacheLevel.Default);
    HttpWebRequest.DefaultCachePolicy = policy;
    // Create the request.
    WebRequest request = WebRequest.Create(uri);
    // Define a cache policy for this request only. 
    HttpRequestCachePolicy noCachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);
    request.CachePolicy = noCachePolicy;
    WebResponse response = request.GetResponse();
    Console.WriteLine("IsFromCache? {0}", response.IsFromCache);            
    return response;
}

myPictureBox.Location = new Point(myPictureBox.Location.X, myPictureBox.Location.Y - 1); // move the Y position up 1 pixel

int certainPoint = 50; // you pick this number
bool hasReachedCertainPoint = false;

...

void MyTimerTickHandler(object sender, EventArgs e)
{
    if (hasReachedCertainPoint == false)
    {
        myPictureBox.Location = new Point(myPictureBox.Location.X, myPictureBox.Location.Y - 1); // move the Y position up 1 pixel
        hasReachedCertainPoint = myPictureBox.Location.Y > certainPoint;
    }
    else
    {
        myPictureBox.Location = new Point(myPictureBox.Location.X, myPictureBox.Location.Y + 1); // move the Y position down 1 pixel
    }
}