Source: https://guthlabs.ai/docs/instruments/wentworth-grain-size-classifier/mechanism/

instrument mechanism / verified-clean

# Wentworth Grain-Size Classifier mechanism

The inspectable method record for Wentworth Grain-Size Classifier, kept separate from implementation and qualification.

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

## Model scope

The logarithmic φ formula and standard Udden-Wentworth classification concept are sound, but the specification needs the inverse formula for φ inputs, an explicit complete lookup table, a boundary convention, and strict positive-diameter validation. The honest label should state that this is a Udden-Wentworth sediment-size classifier, not a complete sedimentological description; shape, sorting, composition, and depositional context are not computed.

- The stated φ = -log2(d_mm) formula is correct when d_mm is a positive numerical grain diameter expressed in millimetres.

- Because the input may be a φ value, the inverse formula d_mm = 2^(-φ) is required but is not stated.

- The Wentworth boundary-inclusion convention is unspecified. The expected categories below assume lower diameter bounds are inclusive and upper bounds are exclusive: [lower, upper). Without that convention, exact boundary inputs such as 1 mm or 0.5 mm are ambiguous.

- The table should explicitly define the full category intervals, including boulder (>256 mm) and clay (<0.00390625 mm).

## Units and conventions

- The logarithm argument is the numerical grain diameter in millimetres; d_mm must be greater than zero.

- A diameter supplied in micrometres or another unit must be converted to millimetres before applying the formula; 1 micrometre = 0.001 mm.

- For φ input, φ is dimensionless and the diameter used for classification is d_mm = 2^(-φ).

- Expected category results use the convention [lower diameter, upper diameter), with the smallest category receiving an exact lower-bound value.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "grain_diameter": 1,
    "unit": "mm"
  },
  "expected_outputs": {
    "phi": 0,
    "class_name": "very coarse sand"
  },
  "reference_data": {
    "rows": [
      {
        "diameter_mm": 1,
        "phi_boundary": 0,
        "class_name": "very coarse sand",
        "source_convention": "Udden-Wentworth grain-size scale, widely tabulated standard value"
      },
      {
        "diameter_mm": 2,
        "phi_boundary": -1,
        "class_name": "granule",
        "source_convention": "Udden-Wentworth grain-size scale, widely tabulated standard value"
      }
    ],
    "boundary_convention": "[lower diameter, upper diameter)"
  },
  "working": "φ = -log2(1.0) = -log2(1) = 0.0. The diameter is at the 1.0 mm boundary and, using [lower, upper), belongs to the 1–2 mm very coarse sand interval."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The zero-diameter input produces an undefined logarithm and must be rejected. The specification also does not explicitly define exact class-boundary endpoint ownership or enforce the diameter unit, creating boundary and unit-convention failure risks.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/wentworth-grain-size-classifier/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/wentworth-grain-size-classifier/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/wentworth-grain-size-classifier/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-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`