Rich / Cheap measures how a bond's market spread compares to the spread its rating alone would imply. We compute: Rich/Cheap (bp) = market G-Spread − rating-implied spread, where the rating-implied spread comes from Damodaran's synthetic-rating table (a benchmark of typical default spreads by S&P/Moody's letter rating). A positive value means the bond pays MORE than its rating implies — it trades CHEAP, with extra compensation for liquidity, EM exposure, idiosyncratic risk, or potential mispricing. A negative value means the bond trades TIGHTER than its rating implies — investors are paying up, often because of scarcity, benchmark inclusion, or perceived credit improvement ahead of an upgrade. The metric is a quick sanity check before buying: a 5y BB corporate trading 200bp tighter than a typical BB benchmark is either a hidden gem or a misrating waiting to be flagged. Caveats: the underlying table is built on US non-financial corporates, so for sovereigns, financials, and EM issuers, the implied spread is a rough proxy — sovereigns typically trade tighter than corporate-equivalent ratings, and EM corporates wider.