The TDD was invented by a deaf physicist Robert Weitbrecht and a deaf orthodontist James C. Marsters in 1964. Before email or texting this was a breakthrough in communications for people with hearing impairments. Like these modern counterparts it had its own vocabulary of commonly used abbreviations for example SKSK now hanging up and XXXX for a typing error. See the first such device in Northern Ireland in action, learn how it works and how it has helped the people who use it.