Source: https://guthlabs.ai/docs/instruments/price-elasticity-of-demand-calculator/implementation/

instrument implementation / implementation-contract

# Price Elasticity of Demand Calculator implementation

A source-bound implementation contract for Price Elasticity of Demand 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**: t5-190

**Effect**: Computation or source lookup only

## Input and validation requirements

An unchanged price makes the percentage price change exactly zero, so the midpoint elasticity quotient is undefined. The instrument must reject that input or explicitly report undefined; returning a numeric result would be incorrect.

## 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": {
    "price_before": 10,
    "price_after": 12,
    "quantity_before": 100,
    "quantity_after": 90,
    "price_unit": "currency units",
    "quantity_unit": "units"
  },
  "expected_outputs": {
    "elasticity_coefficient": -0.578947,
    "classification": "inelastic"
  },
  "working": "Average Q = (100 + 90) / 2 = 95. ΔQ = 90 - 100 = -10. ΔQ / average Q = -10 / 95 = -2/19. Average P = (10 + 12) / 2 = 11. ΔP = 12 - 10 = 2. ΔP / average P = 2 / 11. E = (-2/19) ÷ (2/11) = (-2/19) × (11/2) = -11/19 = -0.578947. Since |E| = 0.578947 < 1, the result is inelastic."
}
````

## Other records

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