Question: How can I know in a C#-Application, in which direction the screen of the mobile device is orientated? (i.e. horizontal or vertical).

Answer: 
In Microsoft.WindowsMobile.Status there is a class which keeps track of all kinds of properties of your device. 
Besides the one you need, DisplayRotation, it also contains properties about phone coverage, Nr of missed calls, next appointment and many more. See [msdn](http://msdn.microsoft.com/en-us/library/microsoft.windowsmobile.status.systemproperty.aspx) for more info. 

You can also add an event-handler to be notified of changes of these properties.
you should add 2 Refrences to the project:
Microsoft.WindowsMobile
Microsoft.WindowsMobile.Status

then you can use this code for determine orientation:

```
int orientation=Microsoft.WindowsMobile.Status.SystemState.DisplayRotation;
if(orientation== 90 || orientation==-90 || orientation==270) //Landscape is 90 or -90 or 270
{
    //your code;
}
else
{
    //your code;
}

```