Source: https://guthlabs.ai/docs/instruments/probability-basics-calculator/implementation/

instrument implementation / implementation-contract

# Probability Basics Calculator implementation

A source-bound implementation contract for Probability Basics 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**: t4-129

**Effect**: Computation or source lookup only

## Input and validation requirements

- Division by zero occurs when P(B)=0; the calculator must reject or clearly report an undefined conditional probability or Bayes result.

- Invalid probabilities below 0 or above 1 must be rejected.

- Inconsistent event inputs can produce misleading results unless bounds such as P(A∩B)≤P(A) and P(A∩B)≤P(B) are enforced when the corresponding values are supplied.

- Expected-value tables with probabilities that do not sum to 1 require rejection or explicit normalization behavior; normalization is not specified.

- Rounding can make a probability table sum slightly above or below 1, so the accepted tolerance is unspecified.

- Infinite or very large outcome tables can make expected-value computation divergent, overflow, or lose precision.

## 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": {
    "P_A_intersection_B": 0.18,
    "P_B": 0.3
  },
  "expected_outputs": {
    "P_A_given_B": 0.6
  },
  "working": "P(A|B)=P(A∩B)/P(B)=0.18/0.30=0.60."
}
````

## Other records

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