Source: https://guthlabs.ai/docs/instruments/rule-of-70-gdp-doubling-time/implementation/

instrument implementation / implementation-contract

# Rule of 70 GDP Doubling Time implementation

A source-bound implementation contract for Rule of 70 GDP Doubling Time; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t5-196

**Effect**: Computation or source lookup only

## Input and validation requirements

A zero growth rate causes division by zero and must be rejected or returned as undefined. Negative growth produces a raw negative quotient that is not a meaningful doubling time and therefore requires an implicit validity branch. The percent-versus-decimal convention can also produce a materially different result if the input unit is misunderstood.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "annual_gdp_growth_rate_percent": 2.5
  },
  "expected_outputs": {
    "years_to_double": 28
  },
  "working": "Apply Rule of 70: years ≈ 70 / growth rate %. Substitute 2.5: 70 / 2.5 = 28. Expected result: 28 years."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/rule-of-70-gdp-doubling-time/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/rule-of-70-gdp-doubling-time/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/rule-of-70-gdp-doubling-time/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`