Apollo user manual Why Calibration is Necessary, Apollo 120/150 159

User Manual version 2007

Why Calibration is Necessary

Calibration is a necessary step for the touchscreen prior for its operation. Unlike mouse or keyboard applications where the cursor is part of the image, a touchscreen is a physical overlay with an independent coordinate system. Only by knowing the position of the image can the PC software convert touchscreen coordinates into image coordinates. Besides, the differences among touchscreens and controllers, calibration also compensates for the variation in video image among displays. The image is affected by horizontal and vertical adjustments on the monitor and by the physical mounting of the touchscreen.

Additional calibration complications include image blooming, where bright-colored images expand, and the "pin cushion" effect, which causes the corners of the display to be stretched. Poor display linearity can cause similar-size boxes to be larger at the edges of the screen than they are in the middle, or vice-versa. The displayed image can also be tilted. Even changing video modes can affect the screen size.

Perfect calibration cannot be achieved in all circumstances. For example, the user can encounter parallax problems with a change in position, or because the present user is not the same stature as the person who calibrated the screen.

Even the most sophisticated calibration techniques can only partially overcome such variations. Therefore, most touchscreen software uses only a two or three-point calibration sequence and relies instead on well-placed touch zones and appropriate user feedback.

The three-point calibration sequence used by Elo automatically corrects inverted touchscreen installations and backward cable connections. X or Y-axis inversion is normal for most touchscreens.

APOLLO 120/150 III 9-159