The book is NOT based on either sheet music sales or record sales. It is based on the amounts of records sent out to record shops. Or shipping figures. For example all the Christmas records, some of which show as top, ALL vanish from the chart after Christmas. The shops stopped ordering them! Or the record companies stopped sending them out. Records were issued in the first week or second week of each month. So the chart fills up with hits those weeks. The book is good for telling you when a record was issued. It tells you how many records were ordered by shops, it doesn't tell you how many each shop sold. Or what the public were buying. Though there is a link between orders and sales. It's not very good at listing the most popular side. And if you look at the record listed in the book, it was clearly the other side of the record that the public were after and the song in the sheet music chart at the time. It has an advantage over the Sheet Music charts in that it features tunes that would not have Sheet Music, such as orchestral tunes, like The Dick Barton Theme!