30 is equipped with a sound system 43 as shown in fig3 it comprises a speaker and circuitry that allows it to play appropriate sounds the vcu 10 instructs the mrs 30 when to emit sound and which sound to play the samples of sound to play are stored in non volatile memory in the sound system 43 indexing system 46 and position marker detector 48 are fig3 used to indicate to the micro controller 44 when the mr 30 has passed over a position marker 58 as shown in fig1 and 4 the indexing system 46 distinguishes the intermediate markers 58 that are placed at zone boundaries from end zone markers i e end of track indicators eoti 57 fig1 eoti 57 consists of more than one usually three marking plates intermediate markers 58 can be attached to the upper 55 and lower 54 wires at any location however they are also used to support wires 55 and 54 at the intermediate posts 56 as shown in fig1 the indexing system 46 uses the position marker detector 48 to detect when an mr 30 is passing over a marking plate 58 or over eotis 57 it comprises a light emitting diode 80 and a light detector 81 which are mounted as shown in fig4 each mr 30 is equipped with two marking plate detectors of which the first is mounted at the front end and the second one is mounted at the rear end of mr 30 for that reason eoti 57 consists of more than one usually three marking plates so that the mr onboard processor 40 can detect an event when light from.