Specified data sets may be tracked from creation to end-of-life. The compounds are useful as photoactive materials. Said control unit may further comprise a control arm for inputting the required direction of movement of said nosewheel; means for transmitting direction information to said self-propelled nosewheel; means for receiving direction information at said self-propelled nosewheel; and means for controlling the direction of said nosewheel. An optional permanent magnet can also be placed on the magnetostrictive pad, which may help increase audibility of said auditory signals.