ICCF numeric notation
ICCF Numeric notation is the official chess game notation for all International Correspondence Chess Federation games.
In Numeric notation all the squares are numbered with a two-digit number. In this simple coordinate system the first digit describes the rank and the second one the file. A move is defined by pairing two of these two-digit coordinates together: the move that would be written 1. e4 in algebraic notation would be written 1. 5254 in Numeric. The pawn starts from square (5,2) and moves to (5,4). Neither the type of the moving piece nor captures are specifically marked in Numeric notation - all moves, except for pawn promotion, consist of only four digits.
In pawn promotion a fifth number must be added: "1" for queen "1", "2" for rook, "3" for bishop and "4" for knight. For instance in the case of a pawn on f7 moving to f8 and promoting to a rook would be 67682. A four digit notation where the starting rank is omitted (because it is always "7") can also be seen: 6682. However, this is confusing and against the standard.
For castling, the king start position and end position are recorded: for white, 5131 (queen side) and 5171 (king side); for black, 5838 (queen side) and 5878 (kind side).