So called due to being originally worn by the GP driver Jo Siffert in 1969 (indeed there is even a picture of him wearing this Chronomatic dial variant). Less than 10 of these have surfaced and along wih the Chronomatic Monaco and the Monaco PVD, they are the most highly prized watches for Heuer collectors.

Chronomatic Autavia "Siffert" 1163T

Siffert Chronomatic RCno1 copy