Simon uses a see-through letter board. His communication partner holds it up between their faces. When Simon looks at a letter, the other person moves the board until their eyes connect together on the letter. The process is continued until Simon has spelt out all his words he wants. Simon see the advantage of people predicting his words, and indeed, sentences, as the flow of conversation is important to him.
His letter board is a unique invention. He saw his college friend using Tobii one which she designed herself and saw how effectively they were using it.