Interferometric scanning method and apparatus for measuring rotationally and non-rotationally symmetric test optics either having aspherical surfaces or that produce aspherical wavefronts. A data access primitive is used to model addressablity for the memory-mapped device. Each arc protruding member is provided on an inner surface of the shielding member that covers the tray as protruding towards an upper surface of the disc placed on the table of the tray. For example to transfer a Giga-bytes sized file could cause a displaying of web based user interface to be blocked and hanged. A lower shroud is aligned with the upper shroud by alignment posts and alignment post receivers and then raised into contact with the steering column.