Pure chocolate products must indicate the percentage of cocoa solids they contain.  This assures the consumer of the proportion by weight of the product which comes from the cocoa bean.  Higher percentages do not necessarily indicate an increase in quality or in bitterness as some cocoas are naturally sweeter than others.  A chocolate which is 40% poor quality cocoa (and 60% sugar) can be very bitter and a premium chocolate which is 60% cocoa (and 40% sugar) can be sweet and fruity.