The VL-1 keys double as calculator buttons. When entering notes into the memory, you use the keys to define pitch and rhythm:
Casio Song Book : Casio Computer Co., LTD. : Free Download, Borrow, and Streaming : Internet Archive. Internet Archive Casio Vl-tone: Song Book with Rhythm and Melody Numbers casio vltone songbook pdf
: "Jupiter" from The Planets , "Amazing Grace," "Greensleeves," and "London Bridge." The VL-1 keys double as calculator buttons