In physics, the fine-structure constant is a fundamental physical constant, namely the coupling constant characterizing the strength of the electromagnetic interaction. The numerical value of is the same in all systems of units, because is a dimensionless quantity. As of 2008, the best determination of the value of the fine- structure constant is = 7.297352569(5)×10 3 = 1/137.035999084(51). The standard error is enclosed in parentheses.