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

instrument mechanism / verified-clean

# Flash Guide Number Calculator mechanism

The inspectable method record for Flash Guide Number Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The core relationship is correct under the stated unit and ISO assumptions. The spec needs an explicit ISO reference for the input GN—normally ISO 100—and explicit same-unit validation before it can receive PASS. The honest label that manufacturer GN ratings are approximate or optimistic should remain visible.

- The GN=aperture*distance relationship is standard, but the stated formulas omit the ISO adjustment; the implementation must explicitly define whether the entered GN is rated at ISO 100 and calculate GN_effective=GN_input*sqrt(ISO/100).

- The spec does not explicitly state that guide number and distance must use the same unit system, such as both meters or both feet.

## Units and conventions

- Guide number and distance use identical units; GN in meters requires distance in meters, and GN in feet requires distance in feet.

- The entered guide number is assumed to be the manufacturer rating at ISO 100.

- ISO scaling uses GN_effective=GN_ISO100*sqrt(ISO/100).

- Aperture is an f-number and is dimensionless for this calculation.

- ISO is a positive numeric sensitivity value.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "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."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

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.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/flash-guide-number-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/flash-guide-number-calculator/implementation/>)[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`

- `BOUNDARY_HAZARD_CATALOG.json`