In 1977 Rolex creates the new caliber 3055 and the reference changes from four to five digits, the last number indicates the material of the case (it moves from the 1800 series to the 18000 series). Here the ref 18078 using burl wood dial and a tree bark styled bracelet and bezel was one of the rarest from this period.  The reference was made from 1981, 1983, 1986, 1987, 1988.