In a flywheel having variable inertia, first and second guide grooves are respectively formed at a body and a rotatable member such that an overlapping position thereof is varied according to a relative rotation thereof. The combined receiver and speaker has a diaphragm, a voice coil, and a chip resistor. The plurality of entitlement tables may have a priority hierarchy, wherein the priority hierarchy defines a higher priority entitlement table as being dominant to a lower priority entitlement table. One method includes providing a light source in a housing and translating a lens arrangement substantially along a light path of a light beam generated by the light source. Some embodiments of the invention may be used to assess the effects of optimising tint for subjects who suffer from visual dyslexia or other impairments of the visual system. In certain instances, at least a portion of the number of particles are each contained within a selective transport member.