Where did the 71 come from? The US inch was 2.54000508 cm and the UK inch was 2.5399977, until the Johansson's blocks convinced everyone to use the industrial inch of exactly 2.54 cm - what is now called the "international inch" (1ft = 0.3048 meters).

A nautical mile corresponds to 2.9229 cm. A survey foot is not much different than an international inch. I hope there's some oddity of history I'm missing!