Source: https://guthlabs.ai/docs/instruments/compressibility-factor-z-estimator/implementation/

instrument implementation / implementation-contract

# Compressibility Factor (Z) Estimator implementation

A source-bound implementation contract for Compressibility Factor (Z) Estimator; 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**: t7-003

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification does not provide the Lee-Kesler/Pitzer coefficients, lookup-table values, interpolation grid, or pressure convention. Consequently, nontrivial numerical Z outputs and the two sides of the interpolation branch switch cannot be reproduced or independently verified. The estimator must also reject Pc=0 and handle P=0 volume correction explicitly.

## 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": {
    "gas": "Methane",
    "P_Pa": 4599200,
    "T_K": 190.56,
    "Pc_Pa": 4599200,
    "Tc_K": 190.56,
    "omega": 0.01142
  },
  "expected_outputs": {
    "Pr": 1,
    "Tr": 1,
    "Z": 0.286,
    "molar_volume_m3_per_mol": 0.00009853
  },
  "reference_data": {
    "Pc_Pa": 4599200,
    "Tc_K": 190.56,
    "omega": 0.01142,
    "source_convention": "NIST Chemistry WebBook / widely tabulated standard methane critical properties",
    "Z0_at_Pr_1_Tr_1": 0.2957,
    "Z1_at_Pr_1_Tr_1": -0.85,
    "source_convention_chart": "Lee-Kesler generalized compressibility chart, standard textbook tabulation"
  },
  "working": "Pr=P/Pc=4,599,200/4,599,200=1.000000. Tr=T/Tc=190.56/190.56=1.000000. Z=Z0+omega*Z1=0.2957+(0.01142*-0.85)=0.2957-0.009707=0.285993, rounded to 0.286. V=ZRT/P=(0.286*8.314462618*190.56)/4,599,200. First, RT=8.314462618*190.56=1,584.404796 J/mol. Then ZRT=0.286*1,584.404796=453.539772 J/mol. Finally V=453.539772/4,599,200=0.00009861 m^3/mol, approximately 9.86e-5 m^3/mol."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/compressibility-factor-z-estimator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/compressibility-factor-z-estimator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/compressibility-factor-z-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-tranche7/tranche7-results.json`