Measure convergence at the same bars
On a linear price scale, write the upper boundary as U(t) = aU + mU × t and the lower boundary as L(t) = aL + mL × t, where t counts bars. Width is W(t) = U(t) - L(t). A rising wedge requires mL > mU > 0 and positive width throughout the formation. Its width decreases by mL - mU price units per bar.
- Higher highs and higher lows are insufficient. A rising parallel channel has both, but no convergence.
- Compare U and L at the same start and end bars. Subtracting a swing low from a swing high on a different bar mixes width with movement along the slope.
- Near-equal slopes need a minimum contraction rule to distinguish a narrow wedge from measurement noise. The numerical threshold below is an example choice.
- Straight lines fitted to logarithmic prices describe different slopes. Keep the price scale and calculation method consistent rather than judging angles from chart pixels.
| Structure | Slope condition | Width |
|---|---|---|
| Rising wedge | mL > mU > 0 | Shrinks while both boundaries rise |
| Ascending parallel channel | mL = mU > 0 | Stays constant |
| Ascending broadening wedge | mU > mL > 0 | Expands |
| Ascending triangle | mU = 0 and mL > 0 | Shrinks beneath a flat upper boundary |