The basic premise of special relativity is that absolute motion is not detectable. Experimentally, this involves only two general cases, (i) detection via mechanical objects and (ii) detection involving light rays. Case ii readily resolves into two sub-cases, ii-a, detection involving round-trip light rays, and ii-b, detection involving one-way rays. Since cases (i) and (ii-a) were experimentally closed prior to special relativity (SR), this left only case ii-b for SR to actively pertain to. SR's prediction in the one-way light speed case is invariance. Specifically, SR predicts that all inertial observers must obtain the exact value c, and only that value, when using two clocks to measure the one-way speed of light. Since this does not happen in the case of slow clock transport, we can immediately eliminate that case. This leaves only the case of two always-mutually-at-rest clocks (in any given inertial frame). This raises the important question, How can SR be tested in that case? That is, how can an inertial observer use two clocks to experimentally measure light's one-way speed?