A flat is a three-legged correction built 3-3-5: wave A divides into three subwaves, B into three, C into five. The difference from a zigzag lies exactly there: in a zigzag A divides into five.
The name misleads. "Flat" sounds like a sideways range, but an expanded flat can run deeper than a zigzag — the form is about structure, not amplitude.
Three kinds by the position of wave B
The kind is set by how far wave B travelled relative to the start of wave A.
Regular. B returns roughly to A's start. The correction looks like a sideways move with even edges.
Running. B falls short of A's start. A sign that the containing move is strong: the correction "runs away" in its direction.
Expanded. B goes beyond A's start. Outwardly this looks like a change of direction, and an expanded flat is what most often derails a count.
The three kinds cover the whole axis with no gaps: B either fell short, roughly reached, or went past. "No kind fits" cannot happen.
The kind does not determine the form
This is the thing to take away. The position of wave B gives the kind of flat, while whether it is a flat at all is decided by the internal build — 3-3-5.
Hence a practical consequence: you cannot say "B went beyond A's start, so this is an expanded flat". First check that A divides into three. If it divides into five, it is a zigzag, however far B travelled.
How it differs from a zigzag
| Zigzag | Flat | |
|---|---|---|
| Build | 5-3-5 | 3-3-5 |
| Wave A | five subwaves | three subwaves |
| Usual depth | deep | sideways to deep |
| What distinguishes it | the build of wave A, not the depth of B |
Where people get confused
Assuming a flat must be sideways. An expanded flat can take price further than a zigzag.
Deciding the form by appearance. Two moves with identical pictures are different forms if their internal builds differ.
Reading an expanded flat as a reversal. When B goes past A's start it seems the correction ended and a new trend began. Then wave C brings price back, and any count built on the "reversal" falls apart.
Why it matters for the count
A flat is a common form for wave 4 inside an impulse, and it is the one that most often creates the false impression that the impulse has ended. Until the internal build is resolved, "the fifth wave has begun" remains a hypothesis.