[geekmaster]

The touch screen is optical, which is why the bezel is raised a bit. The screen is surrounded by photocells and IR LEDs that shine though the black border bezel edges. It senses blocked light just above the screen surface. Be sure to keep your other fingers well away from where you are touching the screen. Is anything (dirt, dust, one of your other fingers) blocking part of the light path?

The touchscreen is "multitouch", but the default behavior is to report a touch screen position midway between two detected touches. An "accidental" extra touch can significantly move the reported touched position.