Source: https://guthlabs.ai/docs/instruments/spur-gear-geometry-calculator/implementation/

instrument implementation / implementation-contract

# Spur Gear Geometry Calculator implementation

A source-bound implementation contract for Spur Gear Geometry 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**: t4-271

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification exposes two hazardous acceptance failures: module m=0 gives a degenerate zero-size gear that should be rejected, and imperial diametral pitch P=0 causes division by zero and undefined outputs. Pressure-angle sign is also not defined, although it does not affect the supplied arithmetic formulas.

## 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": {
    "system": "metric",
    "module_m": 2,
    "N1": 20,
    "N2": 40,
    "pressure_angle_deg": 20
  },
  "expected_outputs": {
    "pitch_diameter_1_mm": 40,
    "pitch_diameter_2_mm": 80,
    "addendum_mm": 2,
    "dedendum_mm": 2.5,
    "outside_diameter_1_mm": 44,
    "outside_diameter_2_mm": 84,
    "root_diameter_1_mm": 35,
    "root_diameter_2_mm": 75,
    "center_distance_mm": 60
  },
  "working": "d1 = mN1 = 2 x 20 = 40 mm; d2 = mN2 = 2 x 40 = 80 mm; addendum = m = 2 mm; dedendum = 1.25m = 1.25 x 2 = 2.5 mm; outside diameter 1 = d1 + 2a = 40 + 2(2) = 44 mm; outside diameter 2 = 80 + 2(2) = 84 mm; root diameter 1 = d1 - 2b = 40 - 2(2.5) = 35 mm; root diameter 2 = 80 - 2(2.5) = 75 mm; center distance = (N1 + N2)m/2 = (20 + 40) x 2 / 2 = 60 mm."
}
````

## Other records

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