This article describes how Surface Capactive technology technology works

Surface Capactive technology is obsolete and no longer available from Elo Touch Systems.

Elo's surface capacitive technology consists of a uniform conductive coating on a glass panel.
During operation, electrodes around the panel’s edge distribute low voltage uniformly across the conductive layer creating a uniform electric field. A finger touch draws current from each corner of the electric field. The controller calculates touch location coordinates by measuring the current and transmits it to the computer for processing.

Below Spec sheet is from 2005 when this technology was sold and Elo's parent company was Tyco Electronics.