The length of the reference path is such that if no sample is present, the two daughter beams will be as perfectly in phase when they meet as they were when they were separated.

ECONOMIST: Microscopy

Although the path was created with reference to as many historical resources as possible, Davidson acknowledged there are inevitably some differences.

BBC: Following in the Bard��s footsteps �C literally

But Mr Lee said it would be "difficult to persuade the North regime to give up the nuclear path", and that North Korea's reference to a "high-level" test could indicate it planned to detonate more than one device.

BBC: S Korea leader warns of 'multiple' N Korea nuclear tests

TUNIS, Tunisia (CNN) -- Arab leaders concluded a two-day summit in Tunisia on Sunday by agreeing to embark on a path of reform "according to our own culture and terms of reference, " Tunisia's foreign minister said.

CNN: Arab leaders pledge reform on their terms