Source: https://guthlabs.ai/docs/instruments/isotope-average-atomic-mass-calculator/implementation/

instrument implementation / implementation-contract

# Isotope / Average Atomic Mass Calculator implementation

A source-bound implementation contract for Isotope / Average Atomic Mass 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**: t5-025

**Effect**: Computation or source lookup only

## Input and validation requirements

- Reject negative abundances.

- Validate that abundances sum to 100% when percentage inputs are used, or 1.0 when fractional inputs are used; otherwise the result is not a valid weighted average.

- If an implementation normalizes abundances by their sum, an all-zero abundance list causes division by zero.

- Require isotope masses and abundances arrays to have equal nonzero length.

- Do not silently mix percentage and fractional abundance representations.

- Built-in isotope data must identify its NIST/IUPAC source, reference composition, and revision because natural isotope abundances can be reference-dependent.

## 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": {
    "isotope_masses_u": [
      34.96885,
      36.9659
    ],
    "abundances_percent": [
      75.78,
      24.22
    ]
  },
  "expected_outputs": {
    "average_atomic_mass_u": 35.45253551
  },
  "working": "Convert percentages: 75.78%=0.7578 and 24.22%=0.2422. Compute 34.96885×0.7578=26.49939453. Compute 36.96590×0.2422=8.95314098. Add: 26.49939453+8.95314098=35.45253551 u."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/isotope-average-atomic-mass-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/isotope-average-atomic-mass-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/isotope-average-atomic-mass-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-tranche5/tranche5-results.json`