Basic principle
The basic principle of DVTT is as below: Place two CCD detectors and infrared ray sender on one side of available area, and place reflecting film on the other three sides to reflect infrared ray. If no object blocks ray, the CCD detectors checkout a complete band. If some object blocks ray in the available area, there would be a invisible area in the band that CCD detectors checkout. Then computer could calculate and find out the exact blocked position by the two CCD detectors in corners.

Technical Advantage
1.Exact position, higher precision.
2.Fast response.
3. It support multi-touch and multi-people operation.
4. Unnecessary for special pen. Any nontransparent thing is available to operate on the whiteboard, such as your finger, pointer etc.. Much easier and more convenient writing.
5. Against scratch. And even scratch occurs on the whiteboard, the normal use would not be affected.

Disadvantage
1. Cost is higher.
2. It may be affected by strong infrared ray.
3. It can't support the right button