Value-weighted index, base 100 at the window start: the sum of the basket's observed values against the prior day's, chained daily, each card's move capped so one outlier can't dominate. Values come from real comparable sales resolved on Slabline card pages. The window deepens automatically as history accumulates. Long-run history reflects the 18 most-traded cards in this basket; the recent window covers all 1,695 tracked cards. Not investment advice.