The VSA reading of how a price bar interacts with the upper (supply) and lower (support) boundaries of a trend channel. It takes effort to penetrate a trend line: low volume approaching support shows no selling pressure and the line holds (path of least resistance is up), while high volume approaching support shows selling pressure and the line may break. The mirror applies at resistance: low volume approaching the supply line shows no demand and the line caps the move; high volume approaching the supply line shows genuine buying effort that may break the line, after which the old resistance becomes new support.