Source: https://guthlabs.ai/docs/instruments/body-surface-area-du-bois/implementation/

instrument implementation / implementation-contract

# Body Surface Area (Du Bois) implementation

A source-bound implementation contract for Body Surface Area (Du Bois); deployment and executable qualification remain separate.

Status: **VERIFIED_WITH_ERRATA**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-with-binding-errata

**Evidence ID**: t2-002

**Effect**: Computation or source lookup only

## Input and validation requirements

The instrument reaches undefined NaN-like results for negative inputs, accepts a mathematically zero but physically invalid weight unless validation is added, and is vulnerable to materially different BSA values when kg/cm versus lb/in conventions are not explicit.

## 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": {
    "weight_kg": 70,
    "height_cm": 170,
    "formula_select": "Du Bois"
  },
  "expected_outputs": {
    "bsa_m2": 1.81
  },
  "working": "BSA=0.007184·70^0.425·170^0.725. 70^0.425≈6.0837. 170^0.725≈41.4071. 6.0837·41.4071≈251.907. 0.007184·251.907≈1.8097 m², which rounds to 1.810 m²."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/body-surface-area-du-bois/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/body-surface-area-du-bois/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/body-surface-area-du-bois/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`