Source: https://guthlabs.ai/docs/instruments/relative-humidity-from-wet-dry-bulb/mechanism/

instrument mechanism / verified-clean

# Relative Humidity from Wet/Dry Bulb mechanism

The inspectable method record for Relative Humidity from Wet/Dry Bulb, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The named Sprung method is standard when the explicit equation, pressure units, ventilation convention, saturation phase, valid input range, and interpolation policy are fixed. Verdict is NEEDS_REVIEW because those implementation-defining choices are not fully specified, especially liquid-versus-ice saturation below 0 C and the exact psychrometric coefficient.

- The Sprung equation is not written explicitly in the specification. The standard water-surface form assumed here is e = e_s(Tw) - 0.00066(1 + 0.00115Tw)p(Td - Tw), with Tw and Td in degrees Celsius and p in hPa.

- Dew-point calculation is not defined beyond saying lookup table; the implementation must specify interpolation method and whether saturation vapor pressure is over liquid water or ice.

- The stated standard-ventilation assumption is incomplete: the psychrometric coefficient depends on ventilation/aspiration conditions, and naturally ventilated, aspirated, and ventilated psychrometers can require different coefficients.

- The specification does not state the valid constraint Tw <= Td. Readings violating this constraint can produce supersaturation or invalid results.

- The specification does not state whether relative humidity is clipped to the physical range 0% to 100% or whether supersaturation is reported.

## Units and conventions

- Temperatures are in degrees Celsius.

- Station pressure is required in hPa for the Sprung coefficient; if supplied in kPa, convert using 1 kPa = 10 hPa.

- Saturation vapor pressures in the reference fragments are hPa and use widely tabulated WMO/standard meteorological values over liquid water.

- The psychrometric coefficient is A = 0.00066(1 + 0.00115Tw), appropriate to the stated standard-ventilation assumption.

- Dew point is obtained by linear interpolation in saturation-vapor-pressure-versus-temperature table entries.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "dry_bulb_C": 20,
    "wet_bulb_C": 20,
    "station_pressure_kPa": 101.325
  },
  "expected_outputs": {
    "relative_humidity_percent": 100,
    "dew_point_C": 20,
    "vapor_pressure_hPa": 23.38
  },
  "reference_data": {
    "saturation_vapor_pressure_hPa": {
      "20_C": 23.38
    },
    "source_convention": "Widely tabulated standard meteorological value; WMO/standard water-surface saturation table",
    "pressure_conversion": {
      "101.325_kPa": 1013.25,
      "source_convention": "SI exact unit conversion"
    }
  },
  "working": "Convert pressure: p = 101.325 kPa x 10 = 1013.25 hPa. Temperature depression: Td - Tw = 20 - 20 = 0 C. A = 0.00066(1 + 0.00115 x 20) = 0.00067518. e = 23.38 - 0.00067518 x 1013.25 x 0 = 23.38 hPa. RH = 100 x e/e_s(20) = 100 x 23.38/23.38 = 100.00%. Since e equals e_s(20), dew point = 20.00 C."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The Sprung calculation accepts physically impossible wet/dry readings that produce negative vapor pressure and a negative logarithm argument; dew point is undefined and the instrument should reject the input. The phase-table boundary and sign/unit conventions also materially affect results.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/relative-humidity-from-wet-dry-bulb/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/relative-humidity-from-wet-dry-bulb/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/relative-humidity-from-wet-dry-bulb/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`

- `BOUNDARY_HAZARD_CATALOG.json`