Accessibility statement

1. Commitment

This site is built to be usable by as many people as possible, including readers using screen readers, keyboard-only navigation, magnification, high-contrast modes or reduced-motion settings. Accessibility is treated as part of the build rather than an audit carried out afterwards, which is the only arrangement that survives changes to the templates.

The target is conformance with the Web Content Accessibility Guidelines version 2.1 at level AA. That target is a working standard rather than a certified status: no external audit has been carried out, and this page states the known limitations honestly rather than claiming a level of conformance that has not been independently verified.

2. What has been implemented

The measures below are present on all thirty pages. They are listed specifically so that a reader can check any of them rather than take a general assurance.

• A skip link as the first focusable element on every page.
• Semantic landmarks: a banner header, a main region, and a content-info footer.
• Exactly one level-one heading per page, with headings in a logical order.
• Visible focus outlines using :focus-visible, never removed.
• A caption on every table describing what the table contains.
• Column scope attributes on every table header cell.
• Text alternatives on every image, describing content rather than filename.
• An accessible name and an aria-expanded state on the navigation control.
• An aria-live region on the calculator results so updates are announced.
• A visible, non-colour-dependent error message on invalid calculator input.
• A reduced-motion rule that disables transitions and smooth scrolling.
• Body text contrast above the 4.5:1 minimum against the page background.
• A layout that reflows to a single column without horizontal scrolling.
• A first-entry dialog with a focus trap that returns focus when dismissed.

3. Colour and contrast

The palette is a charcoal base with a signal-green accent. Body text is a very light grey on charcoal, which exceeds the 4.5:1 minimum for normal text by a comfortable margin. Secondary text is dimmer but remains above the threshold, and the smallest labels on the site are used only for supplementary information that is also available in the surrounding prose.

Colour is never the only carrier of meaning. Links are underlined as well as coloured. Table rows are distinguished by rules rather than by fill. The calculator shows errors as text, not as a red border. The timecode-style labels used throughout as section markers duplicate information that appears in the heading immediately below them.

4. Keyboard operation

Everything on the site can be operated from the keyboard. Tab order follows the visual order of the page. The skip link is the first stop and jumps directly to the main region. The navigation toggle is a button with a state that assistive technology can read. Disclosure sections use the native details and summary elements, so they behave the way a reader’s browser has taught them to expect.

The first-entry dialog traps focus while it is open, cycling forward and backward within the dialog, and returns focus to the element that had it when the dialog is dismissed. Page scrolling is locked while the dialog is open so that a reader using magnification is not moved away from it.

5. Content structure

Long pages are numbered by section, and every numbered section is a genuine heading rather than styled text, so a screen-reader user can move between them directly. The contents rail at the top of long pages is a list of internal links to those sections, marked with an accessible label. Headings are informative rather than teasing: “Detectors and their limits” tells a scanning reader what the section contains in a way that “A word of caution” does not.

Tables are used for genuinely tabular data only, never for layout, and each carries a caption. Checklists are marked-up lists. The calculator is a real form with labelled inputs, numeric constraints and a described error state, and it works without a mouse. The enquiry form on the contact page follows the same pattern: every field carries its own visible label, the required fields are marked as such for assistive technology, and the browser’s own validation messages are left in place rather than replaced by scripted ones.

6. Known limitations

Three limitations are known and stated rather than left for a reader to discover.

• The contents rail on long pages is sticky on large screens. At very high zoom levels it becomes a static block at the top of the article, which lengthens the path to the first paragraph.
• Some comparison tables have five columns and scroll horizontally within their own container on narrow screens. The container is keyboard-scrollable, but reading a wide table on a small screen remains awkward.
• The calculator relies on scripting. Without it, the input fields remain visible and labelled but no result is produced. The formulas are printed on the page so the calculation can be performed by hand.

No external accessibility audit has been carried out. Where a reader identifies a barrier that is not listed here, it will be added to this page whether or not it can be fixed immediately.

7. Technology choices that help

The site is static HTML with one stylesheet and one script served from this domain. There are no hosted fonts, no content delivery network, no embedded video, no iframes, no social widgets and no advertising or measurement tags. Nothing on any page moves, autoplays, flashes or refreshes by itself.

System font stacks are used, which means text renders in a typeface the reader’s own device already provides, at whatever size and rendering settings they have chosen. Pages remain readable with author styles disabled, and the underlying document order matches the visual order.

8. Reporting a barrier

If you encounter a barrier, please write to [email protected] with the subject line “Accessibility”. It helps to name the page, describe what you were trying to do, and say which browser, operating system and assistive technology you were using, including versions where you know them.

Reports are acknowledged where practical and receive a substantive response within five working days. Where a fix is straightforward it is applied and the reporter is told; where it is not, the limitation is added to section 6 of this page with an explanation. This page is reviewed at least once every twelve months and whenever a template changes.

Questions about accessibility