(I) The presence of music has long been known to have a positive effect on supermarket sales. (II) A wide range of products, including music cassettes and CDs, are now available in most supermarkets. (III) Now it has been discovered that varying the tempo of music in stores can affect the speed at which a customer shops. (IV) When the shop is packed, the tempo of the music can be speeded up to encourage shoppers to move quickly through the store. (IV) Similarly, slow music can be played, thus facilitating browsing.