Source: https://guthlabs.ai/docs/instruments/guitar-capo-chart/implementation/

instrument implementation / implementation-contract

# Guitar Capo Chart implementation

A source-bound implementation contract for Guitar Capo Chart; 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**: t6-023

**Effect**: Computation or source lookup only

## Input and validation requirements

The extreme-fret vector exposes unsafe JavaScript integer rounding and the absence of a practical fret-range validation check: mathematical input 9007199254740993 should produce A, but JavaScript Number rounding can make the calculation produce G# instead.

## 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": {
    "open_chord_shape": "C major",
    "open_shape_key": "C",
    "capo_fret": 2,
    "target_key": "E"
  },
  "expected_outputs": {
    "sounding_chord": "D major",
    "sounding_key": "D",
    "alternate_shape_for_target": "D major shape"
  },
  "working": "Use C=0 and E=4. Sounding pitch class=(0+2) mod 12=2 mod 12=2, which is D. Preserve major quality, so the sounding chord is D major. For an E-major target at capo 2: required shape pitch class=(4-2) mod 12=2 mod 12=2, which is D; therefore a D major shape produces E major."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/guitar-capo-chart/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/guitar-capo-chart/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/guitar-capo-chart/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-tranche6/tranche6-results.json`