How long is an 'arm's length'?

INTERNATIONAL PAPERS - Thurs. 07.01.16: North Korea is in the spotlight today after Pyongyang proclaimed it had successfully tested its first miniaturised hydrogen bomb. Should we be afraid of North Korea? Also, the mayor of Cologne draws criticism for advising women to keep "an arm’s length" away from all men to prevent sexual assault. And the New York Times publishes a travel guide for "36 hours in Havana".