Source: https://guthlabs.ai/docs/instruments/frost-date-planting-window-lookup/implementation/

instrument implementation / implementation-contract

# Frost Date & Planting Window Lookup implementation

A source-bound implementation contract for Frost Date & Planting Window Lookup; 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**: t7-066

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification leaves invalid-location handling, lookup-branch precedence, and the sign meaning of frost_date ± offset unspecified. Invalid or missing table rows can therefore yield undefined outputs unless the instrument explicitly rejects them.

## 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": {
    "location_type": "region",
    "region_id": "R1",
    "hardiness_zone": "5b",
    "crop": "tomato",
    "spring_offset_days": 14,
    "fall_offset_days": 7,
    "output_year": 2025
  },
  "expected_outputs": {
    "last_spring_frost": "2025-05-05",
    "first_fall_frost": "2025-10-05",
    "planting_window": {
      "earliest_spring": "2025-05-19",
      "latest_fall": "2025-09-28"
    },
    "frost_threshold_C": 0
  },
  "reference_data": {
    "frost_table_rows": [
      {
        "region_id": "R1",
        "last_spring_frost": "May 5",
        "first_fall_frost": "October 5",
        "source_convention": "NOAA/NCEI 1991-2020 climate-normal-style 32°F frost-date table; dated bundled station/region fixture"
      }
    ],
    "hardiness_zone_row": {
      "zone": "5b",
      "average_annual_extreme_minimum_F": [
        -15,
        -10
      ],
      "source_convention": "USDA Plant Hardiness Zone Map 2023 standard zone band"
    },
    "frost_threshold": {
      "temperature_F": 32,
      "temperature_C": 0,
      "source_convention": "Widely tabulated standard value; water-freezing point at standard atmospheric pressure"
    }
  },
  "working": "Lookup gives last spring frost = May 5 and first fall frost = October 5. Spring date = May 5 + 14 days = May 19. Fall cutoff = October 5 - 7 days = September 28. The frost threshold conversion is (32 - 32) × 5/9 = 0°C."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/frost-date-planting-window-lookup/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/frost-date-planting-window-lookup/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/frost-date-planting-window-lookup/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-tranche7/tranche7-results.json`