BMI Calculator mechanism

Model scope

The arithmetic formula is standard, but the instrument needs an explicit population scope and exact category mapping before release. The existing honest label is appropriate: BMI is an educational screening estimate, does not distinguish fat from muscle, and is not medical advice.

• BMI = mass in kilograms divided by height in meters squared is the standard adult BMI formula and is correct after unit conversion.
• The specification does not define the exact WHO category thresholds or whether categories apply to adults only; pediatric BMI requires age- and sex-specific percentiles rather than fixed adult bands.
• The formula field does not explicitly state the required conversion from pounds to kilograms and centimeters/inches to meters.

Units and conventions

• Weight in kilograms is used directly; weight in pounds is converted using 1 lb = 0.45359237 kg.
• Height in centimeters is converted using 1 cm = 0.01 m; height in inches is converted using 1 in = 0.0254 m.
• Test categories assume adult WHO bands: underweight <18.5, normal 18.5-<25.0, overweight 25.0-<30.0, obesity >=30.0.
• BMI is treated as a screening index, not a direct measure of body-fat percentage or health status.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "weight": 70,
    "weight_unit": "kg",
    "height": 175,
    "height_unit": "cm"
  },
  "expected_outputs": {
    "BMI": 22.8571428571,
    "WHO_category": "Normal"
  },
  "working": "Height: 175 cm x 0.01 m/cm = 1.75 m. Height squared: 1.75 x 1.75 = 3.0625 m². BMI: 70 kg / 3.0625 m² = 22.8571428571. Since 18.5 <= 22.8571428571 < 25.0, category = Normal."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The hazard tests expose undefined behavior for zero height, a physically invalid but arithmetically defined zero-weight boundary, and a severe unit-convention ambiguity. The calculator must reject zero height and require unambiguous units; it should also validate nonpositive body measurements.

Other records

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/batch10-output.jsonl
• BOUNDARY_HAZARD_CATALOG.json