series of four matches in a virtual environment, where the computer-generated board hovered in the air in front of Kasparov, who used special glasses. This was the first man–machine game of chess performed in a completely simulated environment. Manufacture Chessboards have been made from numerous materials over the years, such as ebony, ivory, marble, metal, glass, and plastic. They can also be found as decorative elements in plazas, gardens, and living rooms. High-level games generally use wooden boards, while vinyl, plastic, and cardboard are common for less important tournaments and matches, as well as for home use. Additionally, some very large chessboards are built into or drawn on the ground. Rarely, decorative glass and marble boards are permitted for games conducted by national or international chess federations. Wooden boards are traditionally made of unstained woods that are light brown and dark brown in colour. To reduce cost, some boards are made with veneers of more expensive woods glued to an inner piece of plywood or chipboard. A variety of colour combinations are used for plastic, vinyl, and silicone boards. Common dark-light combinations are black and white, as well as brown, green or blue with buff or cream. For international or continental championships, FIDE's regulations state that wooden boards should be used. For other FIDE tournaments, wood, plastic, or cardboard boards may be used, and the board should be rigid in all instances. The board may also be made of marble, as long as there is an appropriate contrast between the light and dark squares. The finishing should be neutral or frosted but never shiny. The squares should be from 5 to 6 cm in length, at least twice the diameter of a pawn's base. If the table and the board are two separate pieces, the latter must be fixed so it stays in place. Board notation There are various systems for recording moves and referring to the squares of the chessboard; the standard contemporary system is algebraic notation. In algebraic notation, the files are identified by the letters a to h, from left to right from the white player's point of view, and the ranks by the numbers 1 to 8, with 1 being closest to the white player. Each square on the board is identified by a unique coordinate pairing, from a1 to h8. In the older descriptive notation, the files are labelled by the piece originally occupying its