Source: https://guthlabs.ai/docs/instruments/wet-bulb-temperature-estimator/mechanism/

instrument mechanism / verified-clean

# Wet-Bulb Temperature Estimator mechanism

The inspectable method record for Wet-Bulb Temperature Estimator, kept separate from implementation and qualification.

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

## Model scope

NEEDS_REVIEW because the instrument does not define which of the two claimed algorithms is authoritative. For a deterministic plain-arithmetic implementation, explicitly select Stull (2011), document that pressure is ignored, validate T and RH, and label the output as an empirical approximation. Alternatively, specify the complete pressure-dependent iterative psychrometric model and convergence tolerance.

- The specification names two materially different algorithms—Stull (2011) and an iterative psychrometric energy balance—but does not select one or define the iterative equations, psychrometric constants, saturation-vapor-pressure correlation, or convergence criterion.

- The Stull formula does not use barometric pressure, so the declared P input is ignored when that method is selected. Pressure is required for a pressure-aware psychrometric calculation.

- The Stull correlation is an empirical approximation, not a general psychrometric energy-balance solution; its stated approximate validity range and error should be displayed honestly.

## Units and conventions

- Stull inputs are dry-bulb temperature T in degrees Celsius and relative humidity RH in percent from 0 to 100, not a fraction from 0 to 1.

- The Stull formula uses inverse trigonometric functions in radians.

- Barometric pressure P is not used by the Stull formula. If P is intended to affect the result, its units and the complete pressure-corrected algorithm must be specified.

- Outputs are degrees Celsius when T is supplied in degrees Celsius.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "method": "Stull 2011",
    "dry_bulb_C": 20,
    "RH_percent": 50,
    "pressure_kPa": 101.325
  },
  "expected_outputs": {
    "wet_bulb_C": 13.699
  },
  "working": "Use Tw = T*atan(0.151977*sqrt(RH+8.313659)) + atan(T+RH) - atan(RH-1.676331) + 0.00391838*RH^(3/2)*atan(0.023101*RH) - 4.686035. sqrt(50+8.313659)=sqrt(58.313659)=7.63634. First angle: atan(0.151977*7.63634)=atan(1.16055)=0.859571, so T term=20*0.859571=17.1914. atan(20+50)=atan(70)=1.556512. atan(50-1.676331)=atan(48.323669)=1.550105. RH term: 50^(3/2)=353.553; 0.00391838*353.553=1.38536; atan(0.023101*50)=atan(1.15505)=0.857222; product=1.18756. Therefore Tw=17.1914+1.556512-1.550105+1.18756-4.686035=13.6993 C, or 13.699 C. P is unused."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A negative-RH input drives the RH^(3/2) term outside the real-number domain and can yield NaN unless rejected. The specification also leaves the Stull-versus-iterative method and the validity-limit branch unspecified, while RH unit convention can be interpreted as either percent or fraction.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/wet-bulb-temperature-estimator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/wet-bulb-temperature-estimator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/wet-bulb-temperature-estimator/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-tranche6/tranche6-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`