In order for eyetracking measurements to be accurate, the eyetracker needs to know about the monitor you are using - how wide is it? How tall? What is its resolution? This is so that it can translate eye movements (in degrees of visual angle) into usable data (in height, pix, etc. units). Without this information, the eyetracker can only guess and will therefore give only approximate data.
Using the Monitor Centre, configure your monitor settings.