Four units per matra, a fourfold compression of the base statement. Because it is two doublings rather than a new grid, it feels like acceleration rather than recoloring — which makes it the default high-speed layer for kaida development and rela work.
At this rate the limiting factor becomes nikas: strokes must come from the fingers with minimal hand travel. Sequences that run base rate through fourfold and back are a staple test of both hands' evenness.