The illustration below shows the TGUI as it appears on a sample application. All tactile symbols, including those needed to calibrate the device, to identify the overlay to the computer, to control the program and to input data or make choices appear on the tactile drawing itself. By building all of these features into the TGUI, we have greatly simplified the apparatus and the cabling requirements between the TTT and the host computer. For example, an on-board physical numeric keypad would add to the cost of the unit, increase the number of breakable moving parts, and require a separate hardwired connection to the computer. In our TGUI, the outline of a telephone-style numeric keypad appears in raised lines in a standard location on every tactile drawing.
All communication takes place over a single serial connection.
All of these innovations are in the service of reducing cost, limiting points of potential failure, and simplifying installation and use. A start-up routine has been developed that allows quick and precise calibration of the unit each time a new tactile drawing is mounted. The user starts by pressing dot symbols in three corners of the tactile drawing in response to audio instructions. When prompted, the user runs his finger along this raised band from left to right. He will find three dots along this line, which he will press in the order that they are encountered.