Source: https://guthlabs.ai/docs/instruments/exposure-triangle-ev-calculator/implementation/

instrument implementation / implementation-contract

# Exposure Triangle / EV Calculator implementation

A source-bound implementation contract for Exposure Triangle / EV 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**: t4-157

**Effect**: Computation or source lookup only

## Input and validation requirements

A zero shutter-speed input makes the core EV expression undefined and must be rejected. The specification also has no true formula branch, and ambiguous shutter-speed notation can produce a 13.9315685690-stop discrepancy if interpreted incorrectly.

## 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": {
    "f_number": 2,
    "shutter_speed_seconds": 0.25,
    "ISO": 100
  },
  "expected_outputs": {
    "EV100": 4,
    "EV_at_ISO": 4,
    "equivalent_exposure_examples": [
      {
        "f_number": 4,
        "shutter_speed_seconds": 1,
        "ISO": 100
      }
    ]
  },
  "working": "N²=2²=4. t=0.25 s. N²/t=4/0.25=16. EV100=log2(16)=4. ISO adjustment: log2(100/100)=log2(1)=0. EV_at_ISO=4+0=4. Equivalent example: 4²/1=16, matching the original 2²/0.25=16."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/exposure-triangle-ev-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/exposure-triangle-ev-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/exposure-triangle-ev-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`