Source: https://guthlabs.ai/docs/instruments/flash-guide-number-calculator/implementation/

instrument implementation / implementation-contract

# Flash Guide Number Calculator implementation

A source-bound implementation contract for Flash Guide Number Calculator; 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**: t4-205

**Effect**: Computation or source lookup only

## Input and validation requirements

Zero distance produces an undefined aperture and would yield Infinity in unvalidated plain JavaScript arithmetic; negative distance also exposes a sign-convention hazard that can produce a nonsensical negative aperture.

## 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": {
    "operation": "aperture",
    "guide_number": 36,
    "guide_number_unit": "m",
    "iso": 100,
    "distance": 6,
    "distance_unit": "m"
  },
  "expected_outputs": {
    "aperture": 6,
    "effective_guide_number": 36
  },
  "working": "ISO factor=sqrt(100/100)=1. Effective GN=36*1=36 m. Aperture=effective GN/distance=36/6=6, so the required aperture is f/6."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/flash-guide-number-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/flash-guide-number-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/flash-guide-number-calculator/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-tranche4/tranche4-results.json`