The TRU-BEAT reference 6556 was introduced into the market in 1954, powered by the calibre 1040, a modified version of the well-known calibre 1030. Aesthetically similar to a normal Oyster Perpetual, the major difference lies in the "dead beat" centre seconds, where the seconds hand stops at each seconds mark before jumping to the next, performing exactly like the seconds hand of an analogue quartz watch.
"Dead beat" watches surfaced in the early days of watchmaking and have always been synonymous with fine engineering. However, this particularity did not enjoy much popularity upon its introduction, and production was discontinued in a mere five years.
The Tru-Beat model is illustrated in The Best of Time - Rolex Wristwatches by James M. Dowling & Jeffrey P. Hess, p. 202.