# CBB - Cohort Breakeven Birth Year

- Artifact: PictoClarity metric reference
- Canonical HTML URL: https://pictoclarity.com/framework/metrics/cbb/
- Markdown URL: https://pictoclarity.com/md/framework/metrics/cbb/
- Language: en
- Category: Supporting metric

## Summary

A birth-cohort marker for when learned convention overtakes direct object familiarity.

## Definition

CBB marks the modeled birth cohort where learned convention meets or exceeds direct familiarity with the source object.

## Formula Structure

`CBB = min birth year where CLL_y >= DOF_y`

This public formula describes structure, not private calibration.

## What It Reads

- Where a symbol shifts from object familiarity to convention learning.
- How temporal exposure changes meaning transfer.
- Which cohorts are more likely to need labels, context, or alternate symbols.

## High Reading

A later CBB suggests direct object familiarity persists for more cohorts.

## Low Reading

An earlier CBB suggests the symbol depends on learned convention for many users.

## Limits

- CBB is a modeled estimate, not a demographic claim.
- CBB depends on the evidence window and evaluation date.
- CBB is meaningful only when a source object or metaphor has cohort-sensitive familiarity.

## Examples

- A floppy disk save icon has a cohort breakeven because physical disk exposure differs strongly by birth cohort.
- A universal geometric arrow may not need a meaningful CBB when no obsolete source object drives the metaphor.

## Related Metrics

- PCS
- CLL
- NTR
- CTS
- ERS

## Citation Guidance

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