The code is named after Richard Guy, Hugh Blandford and John Roycroft.
The first two devised the original system (the Guy–Blandford code) using different figures to represent the number of pieces.
9 is used if either side has three or more pieces of the same non-pawn type; these positions are possible in standard chess due to pawn promotion.
When indexing or referring to specific positions, rather than generalised material imbalances, the code may be extended in various ways.
With these additions, the position to the right, a draw study by Leonid Kubbel (First Prize, Shakhmaty, 1925), is classified as =0323.12g3g1.