A clear way through.

Navigation and reading

Use the “Skip to content” link at the start of each page to reach the main content. Tab moves between links and controls; Enter activates links and buttons. On phones, open the Menu button to see the site routes. Escape closes the menu, returning focus to its button.

Text can be enlarged using your browser controls. System diagrams resize for the phone layout with full-width selection controls. The ground source buttons change the related explanation, and the question index can show all answers together.

Motion and alternatives

The site follows your device’s reduced-motion preference, removing scroll and hover movement. With JavaScript disabled, navigation and email links remain available, and alternative explanations accompany interactive system views. You can always use the email address directly instead of the draft tools.

Report a difficulty

If something prevents you from using a page, email [email protected]. Include the page, what you were trying to do, and your browser or device if known. This guide describes the controls; it is not a claim of independently certified accessibility compliance.