Gray code is a different genotype(binary)<->phenotype(value) mapping from the standard binary coding. Gray code uses adjacency, so that related phenotypes have genotypes with minimal differences. For example:
| Value | BCD | Gray |
| 0 | 000 | 000 |
| 1 | 001 | 001 |
| 2 | 010 | 011 |
| 3 | 011 | 010 |
| 4 | 100 | 110 |
| 5 | 101 | 111 |
| 6 | 110 | 101 |
| 7 | 111 | 100 |