Source: https://guthlabs.ai/docs/instruments/roof-pitch-rafter-calculator/implementation/

instrument implementation / implementation-contract

# Roof Pitch & Rafter Calculator implementation

A source-bound implementation contract for Roof Pitch & Rafter 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**: t4-055

**Effect**: Computation or source lookup only

## Input and validation requirements

The stated formula has an undefined division when run = 0, and the span-versus-run input representation creates a branch where identical numeric dimensions produce different results. Negative overhang also exposes an unresolved sign convention.

## 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": {
    "run": 12,
    "rise": 6,
    "overhang": 1,
    "unit": "ft"
  },
  "expected_outputs": {
    "pitch_ratio": 0.5,
    "pitch_label": "6:12",
    "angle_degrees": 26.565051,
    "rafter_length": 14.416408,
    "length_unit": "ft"
  },
  "working": "pitch = rise / run = 6 / 12 = 0.5, so the normalized label is 0.5 * 12 = 6, or 6:12. angle = atan(0.5) * 180 / pi = 26.565051 degrees. Base rafter = sqrt(12^2 + 6^2) = sqrt(144 + 36) = sqrt(180) = 13.416408 ft. Rafter length = 13.416408 + 1 = 14.416408 ft."
}
````

## Other records

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