As I worked my way around a very busy Tesco ticking the items of Miss S's list, I eventually found myself in the confectionary aisle searching for the specific % single source chocolate that Miss S had requested - in this case a 74% and an 82% variety. After scanning the shelves in all directions, I decided that the 75% and the 85% versions must be what she was hoping for, even if the figures didn't exactly match - and that those extra few percentage points would make the chocolate perform even better...