Source: https://guthlabs.ai/docs/instruments/depreciation-calculator-straight-line/implementation/

instrument implementation / implementation-contract

# Depreciation Calculator (Straight-Line) implementation

A source-bound implementation contract for Depreciation Calculator (Straight-Line); 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**: t5-130

**Effect**: Computation or source lookup only

## Input and validation requirements

- Useful life of zero causes division by zero and must be rejected.

- Negative or nonnumeric useful life must be rejected.

- Salvage value greater than cost produces negative depreciation and should be rejected or explicitly handled.

- Negative cost or salvage values require validation and should generally be rejected.

- Without a floor at salvage value, rounding or extra elapsed periods can reduce book value below salvage value.

- The currency is unspecified; cost and salvage value must be in the same currency and unit.

- A fractional useful life requires defined treatment for partial-year depreciation and schedule display.

- Rounding policy is unspecified; displayed annual depreciation and book values may not reconcile exactly unless precision is defined.

## 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": {
    "cost": 12000,
    "salvage_value": 2000,
    "useful_life_years": 5
  },
  "expected_outputs": {
    "annual_depreciation": 2000,
    "book_value_schedule": [
      {
        "year": 0,
        "book_value": 12000
      },
      {
        "year": 1,
        "book_value": 10000
      },
      {
        "year": 2,
        "book_value": 8000
      },
      {
        "year": 3,
        "book_value": 6000
      },
      {
        "year": 4,
        "book_value": 4000
      },
      {
        "year": 5,
        "book_value": 2000
      }
    ]
  },
  "working": "Depreciable base = 12,000 - 2,000 = 10,000. Annual depreciation = 10,000 / 5 = 2,000. Book values: year 0 = 12,000; year 1 = 12,000 - (1 × 2,000) = 10,000; year 2 = 12,000 - (2 × 2,000) = 8,000; year 3 = 12,000 - (3 × 2,000) = 6,000; year 4 = 12,000 - (4 × 2,000) = 4,000; year 5 = 12,000 - (5 × 2,000) = 2,000."
}
````

## Other records

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