Methodology

Every answer on OmniCalc is produced by an open, documented method. This page explains where the numbers come from and how they are checked, so you can judge the results for yourself rather than take them on faith.

Conversion factors

Unit conversions use the exact factors set by international definitions, not rounded approximations. The inch is defined as exactly 0.0254 metres, the pound as exactly 0.45359237 kilograms, and the other units follow from the same SI and NIST references. Each system converts through a single canonical base unit — length through the metre, mass through the kilogram — so any pair of units is exact and consistent, and converting one way then back returns the original value.

Temperature is the one affine case: it needs both a scale and an offset (for example, °F = °C × 9/5 + 32), and the engine handles that with the same base-unit model rather than a special path. Results are rounded only for display, using significant digits so small quantities keep their precision and large ones stay readable.

Finance formulas

Financial tools implement standard, published formulas — compound interest with periodic contributions, and loan amortization with the usual monthly-rate convention. Each formula documents its assumptions: how often interest compounds, whether contributions land at the start or end of a period, and how rounding is applied to money. Calculations run in decimal arithmetic to avoid the drift that plain floating-point can introduce over many periods, and every formula is pinned to reference values so a known input always produces the known correct output.

These tools are estimators. They are useful for planning and comparison, but they are not financial advice, and a lender’s own figures may differ because of fees, day-count conventions or rounding rules specific to that product.

Customs rule sets

Vehicle-import calculators are driven by versioned data documents rather than logic buried in code. Each rule set records its version number, an effective date, the source it was drawn from, and the date it was last verified — all of which are shown on the tool so you can see exactly which edition produced your estimate. When rules change, a new versioned document is published alongside the old one instead of quietly overwriting it.

Illustrative rates. The customs figures on OmniCalc are currently illustrative and pending official verification. Treat any import estimate as a rough guide, not a quotation — always confirm the current duty, excise and fees with the relevant customs authority or a licensed broker before you rely on a number.

As the customs data matures we plan a two-person publish step: no rule-set change goes live until a second reviewer has checked it against the cited source. Until that process and the official verification are in place, the illustrative-rates label stays.

Testing discipline

The computation engine is plain, side-effect-free TypeScript, which makes it straightforward to test thoroughly. Three kinds of test guard it:

Unit tests pin individual functions to known correct outputs — for instance, that 1 kilometre is 0.621371 miles.
Property tests assert invariants that must hold for every input, such as round-trip conversions returning the original value within tolerance.
Golden cases lock in worked examples end to end, so a change that would alter a published answer fails the build instead of shipping silently.

Corrections

If a factor, formula or rate looks wrong, it probably matters to someone else too. The honest position is that the customs rates are illustrative until verified, and the rest is held to reference values you can check. You can read more about the product and its principles on the about page.

Conversion factors follow international definitions (SI / NIST). Last reviewed 2026-07-01.