The field descriptions that apply to adult matches are described below. Because of the role of the British football associations in the history of the game, the dimensions of the field of play were originally formulated and expressed in imperial units. Since 1997, the Laws of the Game have preferred metric units, with imperial equivalents given only in brackets. Because the actual values have, in general, not changed since the early twentieth century, they tend to be round numbers in imperial units (for example the width of the goal, unchanged since 1863, is 8 yards or 7.32 metres). Use of the imperial values remains common, especially in the United Kingdom.