How We Verify Our Calculators

A photography calculator is only useful if the maths behind it is right. Every figure on this site is traced back to its source: the published optical formula, the industry standard, the manufacturer datasheet or the official UK rate it comes from. This page explains the process we follow, from first authoring through repeated correctness audits.

The process

✓Figures are traced to named source categories: established optical and astronomical formulae (depth of field, the 500 rule, sidereal rate), industry standards such as CIPA DC-002 for battery ratings, film manufacturer reciprocity data from Ilford, Kodak and Fujifilm, and UK government figures such as HMRC approved mileage rates.
✓Every calculator is tested against hand-worked examples with expected answers derived independently of the code, run as an automated test suite across desktop and mobile browsers before each deployment.
✓Calculators go through adversarial re-checking: a separate review re-derives each result from the underlying formula or source and compares it back to the calculator output, rather than assuming the existing figure is right.
✓When a re-check disagrees with the calculator, we fix the calculator and then verify the fix again before it goes live.
✓Errors reported through the feedback buttons are investigated against the primary source, fixed where confirmed, and re-verified before redeployment.
✓Content is reviewed when sources change, for example when HMRC updates its mileage rates or a manufacturer revises a datasheet, and each calculator carries a last-updated date.

Verified, not guaranteed

Our calculators give estimates, not professional advice. Real-world results vary with your specific camera, lens, conditions and shooting style, so treat outputs as planning figures and confirm capacities and quantities against your own equipment before an important shoot. For the business calculators, figures such as pricing, depreciation and mileage are starting points only; confirm tax treatment with an accountant or with HMRC guidance directly.

Spotted an error?

Every calculator page has feedback buttons. If a figure looks wrong, tell us what you entered and what you expected: we investigate against the original source, fix anything that fails the check, and re-verify before the correction goes live. When a report shows a genuine error, the fix lands on the affected page itself, with a dated correction note where it matters.