Source: https://guthlabs.ai/docs/instruments/heart-rate-zone-calculator/implementation/

instrument implementation / implementation-contract

# Heart Rate Zone Calculator implementation

A source-bound implementation contract for Heart Rate Zone 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**: t4-223

**Effect**: Computation or source lookup only

## Input and validation requirements

An extreme but syntactically numeric age such as 1e308 can produce a finite negative HRmax and entirely negative zone values instead of being rejected. Age zero is also accepted arithmetically despite being an invalid real-world demographic input.

## 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": {
    "age_years": 30,
    "method": "percent_HRmax",
    "resting_HR_bpm": null
  },
  "expected_outputs": {
    "HRmax_bpm": 190,
    "zones_bpm": [
      {
        "zone": "50-60%",
        "range": "95 to <114"
      },
      {
        "zone": "60-70%",
        "range": "114 to <133"
      },
      {
        "zone": "70-80%",
        "range": "133 to <152"
      },
      {
        "zone": "80-90%",
        "range": "152 to <171"
      },
      {
        "zone": "90-100%",
        "range": "171 to 190 inclusive"
      }
    ]
  },
  "working": "HRmax = 220 − 30 = 190 bpm. Zone boundaries: 190×0.50 = 95; 190×0.60 = 114; 190×0.70 = 133; 190×0.80 = 152; 190×0.90 = 171; 190×1.00 = 190. Therefore the five intervals are [95,114), [114,133), [133,152), [152,171), and [171,190]."
}
````

## Other records

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