# cusp (threshold)

a parameter whose window overlaps with another, where the crossing leads into the second rather than ending the first

- Computed level: L14 (depth in the emergence graph, not abstraction)
- Status: review  ·  Domain: window  ·  Arena: ontological

## Emergence
**Emerges from:** [parameter](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-parameter.condition), [window](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-window.range), [wall](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-wall.range-end), [drift](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-drift.aimless), [cross](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-cross.symbol), [first](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-first.order), [lead](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-lead.guide), [rather](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-rather.comparative), [second](https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-second.temporal)

**Through:** The drift of a parameter toward a wall of its window coincides with the opening of an adjacent window, and the crossing of the boundary leads into the second state rather than terminating the first.

**Novel properties:**
- transition priority
- asymmetric window crossing
- concurrent persistence and change

## Examples
- In 2007, the Arctic sea ice extent dropped below 4.2 million km², crossing a threshold scientists now associate with irreversible summer melt trends. *(climate)*
- The Therac-25 radiation therapy machine allowed parameter drift in beam intensity until a software threshold was crossed, delivering lethal doses. *(engineering)*
- Bitcoin’s block reward halving in May 2020 crossed a profitability threshold, triggering a shift in mining pool dominance from China to Central Asia. *(economics)*

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*Canonical: https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-cusp.threshold*  
*Structured data: https://emergencemachine.com/tools/lexicon/what-is-the-meaning-of-cusp.threshold.json*  
*Every definition provably resolves to space, time, energy and pattern.*