Contributions are attributed per day and geometrically linked (Cariño), so the grouping rows sum to the book’s compounded total rather than to the smaller arithmetic sum of daily returns. A name held through two groupings at once is split between them by the weight each one bought, never counted twice and never assigned to one arbitrarily. Excess is the column to read when asking whether a grouping did anything: it is the contribution minus what the same weight would have earned in SPY on exactly the days that grouping was held. The model runs on the Mac (admin/modeling.sh --apply); this page only draws what it uploaded.