Sinn introduced the Einsatzzeitmesser (EZM) line of special-purpose watches in 1997 with this EZM 1 and the Sinn EZM 2. It is an unusual chronograph with left-side crown and pushers and no subdials. The chronograph minute and seconds counter are centrally-located hands, along with running hours and minutes. The date is in a small window at 3 30.
The case, Reference 503, measured 40 mm in diameter and was 16.5 mm thick. It housed the Lemania 5100 chronograph movement.