The Imperial Standard Wire Gauge, which has been sanctioned by the British Board of Trade, was formulated by J. Latimer Clark. Following one of its recommendations, it differs from pre-existing gauges scarcely more than they differ among themselves, and is based on a rational system, the basis being the circular mil. No. 7/0, the largest size, is 0.50 inches (500 mils or 12.7 mm) in diameter (1570 circular mils circumference), and the smallest, No. 50, is 0.001 inches (1 mil or ) in diameter (80 circular mils area). Between each step the diameter, or thickness, diminishes by 10.557%, and the area and weight diminish by ~ 20%.