GBR code

The GBR code or Guy-Blandford-Roycroft code is a system of representing the pieces on the board in a chess position. It is most usually used in endgames and especially in indexing endgame studies.

The basic code consists of four digits, followed by a full stop, and two further digits. The first four digits represent the number and colour of queens, rooks, bishops and knights respectively; each white piece has the value 1, and each black piece the value 3; adding these numbers together gives the digit used in the code. For example, if there are two white rooks and one black rook, the digit used is 1+1+3=5. If there are no other pieces on the board, this will be represented in the code as 0500. If there are more than two of a particular king of piece of a particular colour (as might happen after pawn promotion), the value 9 is used. So if, for example, there is a white queen, two black rooks, two white bishops, two black bishops, and three black knights, the first four digits of the code will be 1689.

The last two numbers of the code are equal to the number of white pawns and the number of black pawns respectively. So if there are four white pawns and seven black pawns, the last two digits of the code are 47.

The code is sometimes used to refer to a particular material balance when talking about endgame theory; for example, the endgame of two knights against pawn (as famously analysed by A.A. Troitzky, leading to his discovery of the Troitzky line), is class 0002.01.

	a	b	c	d	e	f	g	h
8	g1 3 0								8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

When indexing or referring to specific positions, rather than generalised material imbalances, the code may be extended in various ways. Two common ones are to prefix a + to indicate the stipulation "White to play and win" or a = for "White to play and draw"; and to suffix the position of the white and black kings. With these additions, the position to the right, a draw study by Leonid Kubbel (First Prize, Shakhmaty, 1925), is classified as =0323.12g3g1 (the solution is 1.Bf2+ Kh1 2.h7 c2+ 3.Be3 Rxe3+ 4.Kf2 Rh3 5.Bd5+ cxd5 6.hxg8Q Rh2+ 7.Kf3 c1Q 8.Qg2+ Rxg2).

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; the suggestion to count one for a White piece, three for a Black, was made by Roycroft as a means of making the code easier to memorise.