How the Job Lab calculations work

What deterministic means

Job Lab calculators are deterministic, not recommendation models. For a fixed registry version, the same validated inputs follow the same formula, comparison boundaries, rounding display and stop rules. No artificial intelligence chooses equipment, interprets a photograph or fills gaps from similar jobs.

Calculation runs locally in the browser. The launch build has no calculation API, account database or server form. This architecture supports repeatability but does not make an entered value representative. A precise output built from the wrong vibration magnitude, power rating or material remains the wrong record.

Determinism also means there is no hidden product catalogue or supplier rate. If a tool needs a capacity, threshold, usable factor or price, that value is either sourced in the registry or entered and echoed. The output can therefore be reconstructed from the record.

Each print record identifies inputs, assumptions, result, warnings, source keys, research date and registry version. The printed date is simply when the record was printed; it is not the method research date or a source publication date.

Three evidence layers

Law and regulator guidance. Legislation supplies statutory formulae or exposure values where cited. HSE explains duties, methods and task controls. Guidance is not described as law, and an HSE link does not certify a work method.

Manufacturer and technical data. Product pages, manuals and technical publishers support model/range values, rating distinctions or engineering inputs. They remain source-specific. A 162 mm handheld coring range, 3.3/1.65 kVA transformer example or generator application rule is not promoted to a universal threshold.

Conservative Job Lab policy. Fail-closed boundaries, a controlled routing table and any user-entered margin are publication/planning rules. They are labelled policy rather than legislation. Elementary arithmetic—addition, division, energy conversion and rounding up—has no invented external authority.

A source class describes provenance, not strength for every possible claim. Manufacturer data may be authoritative for its own model yet irrelevant to another model. HSE guidance may explain a control route without supplying a numeric product limit. Each citation is scoped in nearby prose.

Evidence markers sit beside consequential claims in guides. The source register groups keys by tool and renders one canonical record with truthful date labels.

Tool classifications and allowed language

Statutory exposure calculation describes HAVS because its daily formula and values are directly tied to legislation. Noise is labelled an exposure record: it uses the statutory energy relationship, while the entered levels and periods still require assessment.

Planning estimate covers transformer, generator, voltage drop, battery, compressor, consumables and hire-duration arithmetic. It reports a calculated quantity under entered assumptions. Fit check covers grinder and core-drill gates; control prompt covers the bounded dust table.

Outputs may say calculated, estimate, numeric gate passed/failed, provisional route, requires confirmation, outside configured range or result suppressed. They do not say safe, suitable, compliant, approved, certified or guaranteed. A passed numeric gate is only that gate.

Formula and units register

All threshold and capacity comparisons use unrounded values. The displayed precision below is presentation only.

Symbols are defined in the relevant guide/tool. In particular, transformer/generator P is electrical input kW and PF is power factor; cable K follows the entered mV/A/m source convention; compressor flow is free-air delivery (FAD) at required pressure.

Unit conversion occurs only where it is explicit. Hours and minutes, millimetres and metres, watts and kilowatts are not interchangeable by field naming alone. Inputs reject non-finite values, impossible date order and percentages outside the published bound before calculation.

Precision and rounding

Intermediate arithmetic stays at JavaScript number precision and is checked for finite values. Boundaries use that unrounded value. A number displayed as 3.183 kVA is not compared as 3.18, and a disc rim speed displayed to two decimals is not rounded before its independent gate.

Display precision follows the register so records are readable without suggesting measurement accuracy that was never supplied. Counts that must be whole—consumable units and calendar days—use explicit integer rules. Consumables round upward only after quantity, yield and waste arithmetic. Optional hire price ratio displays one decimal and always retains “at the prices you entered”.

Rounding never selects a standard product size. Transformer and generator outputs remain quantities for comparison with verified continuous/rating information.

Displayed trailing zeros are intentional where they communicate the register’s presentation precision, not measurement certainty. A source instrument may justify fewer significant figures; the user must not infer laboratory accuracy from the calculator’s decimal places.

Validation, fail-closed and stop conditions

A missing, invalid, contradictory or unsupported input produces “cannot compute without —” or “result suppressed”. The affected number/route and its print control are withheld. Values must be finite, in declared units and within input bounds; an empty row does not become zero where zero changes meaning.

Fail-closed scope is local. If one generator location answer stops sizing, no hidden kVA remains in print. If one grinder gate lacks data, the combination is not shown as passed merely because diameter is known.

Recovery is tested too. After an invalid entry suppresses a result, correcting every required field must produce a fresh result from current values, with stale warnings and earlier numbers removed. Reset must return the form and status to the documented initial state.

Testing and worked vectors

Formula modules have unit tests for valid examples, empty/invalid values and boundary behaviour. Browser flows exercise the rendered form, errors, recovery, print control and local-only network state. Builder equivalence compares composed records with individual-tool outputs for identical inputs.

• HAVS: 5 m/s² × 2 h plus 10 m/s² × 0.5 h = 200 points and A(8) 3.536 m/s².
• Noise: 88 dB(A) × 2 h plus 94 dB(A) × 0.5 h = LEX,8h 84.98 dB(A).
• Transformer: documented inputs = 2.653 kVA running and 3.183 kVA with entered 20% margin.
• Generator: 2.778 kVA running, 5.444 kVA declared start peak and 6.533 kVA with entered 20% margin.
• Battery: 18 V × 5 Ah, 80% usable, 360 W and 40% duty = 12 trigger minutes / 30 elapsed.
• Compressor: documented FAD rows = 8.0 CFM demand / 9.6 CFM with margin.
• Grinder: 71.99 m/s example; 35 mm required against 33 mm maximum fails depth.
• Consumables: ceil((86/12)×1.15)=9. Hire Monday–Thursday is four inclusive days; £400/£45 = 8.9 weeks.

Golden vectors detect drift; they do not prove every real input or work method. Accessibility/browser release checks cover keyboard, focus, 390 px and 340 px widths, no-JavaScript readability, outbound links, runtime requests and print pagination.

Boundary vectors include equality, just below and just above where law or a declared gate uses a threshold. Property-style cases check monotonic relationships where expected, such as more trigger time not reducing HAVS exposure, while explicit stop tests prove hazard suppression occurs before route output.

Static-build tests then check all owned routes for one H1, exact metadata/canonical, indexability, source-anchor resolution and required internal links. A no-JavaScript browser context confirms that editorial content is server-rendered. Runtime observation fails on console errors, failed first-party requests or any third-party resource. Print checks use representative long pages because a screen-readable table can still clip or split badly on paper.

Testing evidence identifies the artifact and command. A later content or CSS change invalidates earlier screenshots and PDFs, so the affected checks are repeated against the rebuilt output.

The release report records route coverage and unresolved source gaps so a passing count cannot hide a withheld claim or incomplete integration check.

Dates, versions and change control

Research date is when Job Lab checked a method and source set. Accessed date is when a URL was retrieved. Effective/in force is reserved for verified legislation commencement. Source-owned dates are labelled published, issued, edition or updated; an accessed date never substitutes for publication.

Every formula module carries a semantic registryVersion, researchedDate, source keys and an effective date only where statutory. Version 1.0.0 is the launch registry described here.

A patch changes copy or test clarification without numerical/routing change. A minor version adds a backward-compatible input or source-backed route. A major version changes formula, threshold, classification, unit or routing behaviour.