 In principle, there can be more than one such code for a given word length, but the term Gray code was first applied to a particular binary code for non-negative integers, the "binary-reflected Gray code", or BRGC, the four-bit version of which is shown above.Reflected binary codes were applied to mathematical puzzles before they became known to engineers.Martin Gardner wrote a popular account of the Gray code in his August 1972 Mathematical Games column in Scientific American.