Source: https://guthlabs.ai/docs/instruments/wallpaper-roll-calculator/implementation/

instrument implementation / implementation-contract

# Wallpaper Roll Calculator implementation

A source-bound implementation contract for Wallpaper Roll 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**: t3-019

**Effect**: Computation or source lookup only

## Input and validation requirements

A zero wall height combined with zero pattern repeat makes the effective strip length zero, causing division by zero and an undefined roll count; the calculator must reject the 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": {
    "wall_perimeter_m": 16,
    "roll_width_m": 0.53,
    "wall_height_m": 2.4,
    "repeat_waste_m": 0.3,
    "roll_length_m": 10.05,
    "total_strips_needed": 31
  },
  "expected_outputs": {
    "strips_per_roll": 3,
    "rolls_required": 11
  },
  "working": "Cut length per strip = 2.4 + 0.3 = 2.7 m. Strips per roll = floor(10.05 / 2.7) = floor(3.7222...) = 3. Total strips from wall width = ceil(16 / 0.53) = ceil(30.1886...) = 31. Rolls required = ceil(31 / 3) = ceil(10.3333...) = 11."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/wallpaper-roll-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/wallpaper-roll-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/wallpaper-roll-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-tranche3/tranche3-results.json`