According to the help is the argument to the Pan method:
"PanFactor Optional Double. Amount to pan, expressed as a fraction of the screen width or height."
In my simple English I translate it that a value of 1 is the height resp width of the viewed map in pixels. But this seems not to be true. Also the pan in horizontal direction is depending on the current latitude. For example this value between 1..2 to get more or less half width panning.
Does someone know the exact calculation of the pan factor ?