Seems as though you will need a way to know the area of the screen and then preset speeds for display sizes for the program to go with such as a smaller area screen it would get from one side to the other in 1 second at a slower rate then a large screen which the object would move faster across the screen to get to the other side within that same 1 second. My thoughts on this are that for small displays the game or whatever it is will appear to run slower and on larger screens faster. Thinking you need to either have the user specify a screen size or have some sort of hardware detection for size of display to be part of the equation.