Source: https://guthlabs.ai/docs/instruments/body-fat-estimator-us-navy-method/mechanism/

instrument mechanism / verified-clean

# Body Fat % Estimator (US Navy method) mechanism

The inspectable method record for Body Fat % Estimator (US Navy method), kept separate from implementation and qualification.

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

## Model scope

The listed test vectors use the commonly published US Navy equations as an explicit assumption, but the catalog specification must state the exact equations, base-10 logarithm, units, supported sex categories, domain validation, and required body-weight input before this instrument can be approved. The existing honest label is appropriate but should also state that the estimate is sensitive to measurement technique and is not a clinical body-composition measurement.

- The specification does not provide the actual sex-specific formulas, logarithm base, measurement units, or input sign/domain constraints.

- The standard US Navy body-fat formula requires waist minus neck for men and waist plus hip minus neck for women; these required expressions and sex-specific coefficients are not stated.

- Lean mass cannot be estimated from the listed inputs because body weight is missing. If intended, the usual formula is lean mass = body weight × (1 - body-fat percentage / 100).

## Units and conventions

- The standard US Navy equations use inches for waist, neck, hip, and height.

- The logarithm is base 10, not the natural logarithm.

- Metric inputs must be converted to inches before applying the standard equations: inches = centimeters / 2.54.

- Sex must be restricted to the categories supported by the selected Navy equations; the specification does not define this mapping.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "sex": "male",
    "waist": 34,
    "neck": 15,
    "height": 70,
    "units": "inches",
    "body_weight": null
  },
  "expected_outputs": {
    "body_fat_percent": 17.51,
    "lean_mass_estimate": null
  },
  "working": "Male Navy formula assumed: BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. waist − neck = 34 − 15 = 19. log10(19) ≈ 1.278754. 86.010 × 1.278754 ≈ 109.9856. log10(70) ≈ 1.845098. 70.041 × 1.845098 ≈ 129.2325. BF = 109.9856 − 129.2325 + 36.76 = 17.5131% ≈ 17.51%."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The specification exposes invalid-domain boundary cases that require explicit rejection, and it does not state the formula's required inch units even though unit misinterpretation changes the estimate substantially. The declared lean-mass output is also undefined without a body-weight input.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/body-fat-estimator-us-navy-method/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/body-fat-estimator-us-navy-method/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/body-fat-estimator-us-navy-method/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-tranche2/tranche2-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`