因為美國和全世界唱反調 , 大家早就放棄英制改用公制 . 英制本身在細分時又有十進制和二進制兩種細分法 .

舉例而言 : 1 mil = 0.001 inch = 0.0254 mm , 5/16" = 5/16 inch = 0.3125 inch , 0.3" = 0.3 inch .... ,

http://www.answers.com/topic/mile
1 mile = 5,280 feet or 1,760 yards (1,609 meters)

1 nautical mile = 1 nm = 1,852 meters (about 6,076 feet) = one minute of arc of a great circle = 由地心取一秒弧度所截取的地球圓周長

http://www.answers.com/nautical%20mile
A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet). Also called sea mile.

one minute of arc (1 MOA)
http://en.wikipedia.org/wiki/Minute_of_arc
1 complete circle = 360° = 21,600′ = 1,296,000″
1″ = 1/60 ′ = 1/3600 ° = 1/1296000 of a complete circle

嗯 ! 如果沒有非凡的記憶/理解能力 , 還是老老實實用十進制的公制 (SI) 吧 !