A chart that closes a new bar after a fixed number of contracts have traded, independent of clock time. For example, a 5,000-volume chart in the ES closes a bar every 5,000 contracts. The advantage is that each bar carries approximately equal volume, making cross-bar footprint comparison meaningful and making absorption (lots of volume in a narrow price range) easy to spot; the disadvantage is that the price range per bar varies enormously. Typical settings: ES 3,000–10,000; CL 1,000–5,000; 6E 2,000–8,000.