 A variation with three cubes providing English abbreviations for the twelve months is discussed in a "Scientific American" column in December 1977.One solution of this variation allows displaying the first three letters of any month and relies on the fact that lower-case letters "u" and "n" and also "p" and "d" are inverses of each other.A number of variations are manufactured and sold as souvenirs, differing in the appearance and the existence of additional bars to set the current month.