How does POS retail tills work, cash registers with touch screens how do they work?
They are also known an point of sale and kiosks like the ones in mcdonalds or leisure centres

Touch screens can use one of 3 technologies that I know of:

1. Your actually pushing on a transparent metallic contact like (ITO or ZnO)
2. Your finger is changing the capacitance of a particular area of the screen. Again, transparent contacts are used.
3. There is an infared grid of sensors and receivers on the face of the CRT. Putting yor finger in the way blocks a X and Y co-ordinate(s).

Most now are likely technology #2.

I'm glad someone answered her plea for help. She's posted the same question on four forums, them split...