Separate downward slope from narrowing width
On a linear price scale, let U(t) = aU + mU × t be resistance and L(t) = aL + mL × t be support, where t counts bars. Width is W(t) = U(t) - L(t). A falling wedge requires mU < mL < 0 and W(t) > 0. Width changes by mU - mL each bar, so it shrinks when the upper slope is more negative.
- Compare the two line values at the same bar. Subtracting a low from a high recorded on a different bar does not measure the vertical width.
- Nearly equal slopes can produce negligible contraction. Choose a minimum width reduction before examining the results.
- Chart zoom changes visible angles. Logarithmic price coordinates also change the line equations; keep the display scale and detector calculations consistent.
| Structure | Slope relationship | Consequence |
|---|---|---|
| Falling wedge | mU < mL < 0 | Both lines fall and width shrinks |
| Descending parallel channel | mU = mL < 0 | Both lines fall at the same rate |
| Descending broadening wedge | mL < mU < 0 | Support falls faster and width grows |
| Descending triangle | mU < 0; mL = 0 | Support is flat rather than falling |