High Quality Content by WIKIPEDIA articles! When using the term `the speed of light` it is sometimes necessary to make the distinction between its one-way speed and its two-way speed. The "one-way" speed of light from a source to a detector, cannot be measured independently of a convention as to how to synchronize the clocks at the source and the detector. What can however be experimentally measured is the round-trip speed (or "two-way" speed of light) from the source to the detector and back again. Albert Einstein chose a synchronization convention (see Einstein synchronization) that made the one-way speed equal to the two-way speed. The constancy of the one-way speed in any given inertial frame, is the basis of his special theory of relativity although all experimentally verifiable predictions of this theory do not depend on that convention. Experiments that attempted to probe the one-way speed of light have been proposed, but none has succeeded in doing so. It was later shown that these experiments are in fact measuring the two-way speed.