Tru-Beat 6556, ‘50s Stainless steel round case, n.139412, stainless steel smooth bezel. Argenté dial, applied indexes. Automatic movement, cal.1040 with dead-beat seconds. Stainless steel riveted Oyster bracelet. Size: 35 mm. Notes: The Tru-Beat model was launched in 1954 as a tool watch for doctors and healthcare professionals. It is the only mechanical Rolex reference to ever incorporate a “dead-beat” seconds mechanism, that advances the seconds hand only once per second like a quartz movement (permitting a more accurate reading of patients’ pulse rates).