Shelf-share weights every mention by where the brand sits in the answer, so the shelf adds up to 100%. Named first on a short shelf is worth far more than named fourth on a long one.
Visibility ignores position — simply how often a brand is named. Divide shelf-share by visibility and you get how much of the shelf a brand takes when it does appear.
No brand named is the share of answers that recommended no identifiable brand at all — advice, or retailers only.
Movement shows only where a week-over-week change is larger than the variation between readings. Most weeks, most brands are steady.