A pivoting hub nut, or hub clamp, for manually securing an object to a rotatable shaft provides a first hub defining a first radial slot and a second hub pivotally attached to the first hub defining a second radial slot. According to the invention, the angle of incidence formed relative to a direction that is perpendicular to the measuring surface, at which the second radiation device radiates onto the measuring surface, is no more than 50\xb0. The data obtaining module includes an image sensing module including a charge-coupled device sensor for capturing an image of a light distribution of an LED to be tested, a data reading module and a computing module.