The motive force for a fairground organ is typically wind under pressure generated from mechanically powered sets of bellows mounted in the base of the instrument. The instruments, designed to be operated without a human performer, are keyboard-less apart from a few one-off examples. The organ is played mechanically by either a rotating barrel with the music pinned thereon like a music box, a strip of cards perforated with the musical data and registration controls called "book music", or interchangeable rolls of paper similarly programmed called "music rolls". However, "Victory", pictured above, while a traditional mechanism plays traditional books, it also contains a Yamaha MIDI interface and is most often played electronically – with a blank card in place of the traditional book. Owner Willem Kelders uses this interface to link organs ("Rhapsody" and "Locomotion", driven by "Victory") together so they all play the same music perfectly synchronised.