One control in the header turns every annotated column header's glossary sentence into text on the page, and the setting is remembered in the browser rather than on your account.
Explain mode turns the site's glossary from something you have to hover for into text on the page. It is one control in the header, it changes no figure, and it is remembered per browser rather than per account.
The control
The Explain the figures button sits in the header beside the search control. It is a pressed or unpressed toggle rather than a link, so it reports its state to a screen reader: pressed means explain mode is on. Press it once to turn explain mode on and again to turn it off.
What it reveals
Every table header the site annotates carries a glossary sentence. With explain mode off, that sentence is present in the page but not visible — it is available to a screen reader, and a pointer resting on the header shows it as a tooltip. With explain mode on, the same sentence is printed under the header as a small line in the muted text colour, so a column explains itself without a pointer.
Two things it does not do. It adds no explanation where there is no term: a header with no glossary entry stays exactly as it was. And it changes no figure, sort order or filter — the numbers are the same numbers, read with their definitions attached.
Where the setting lives
The setting is stored in your browser, not on your account. It is written to local storage under one key and read back before the page paints, so a page you reload or navigate to comes up already in the mode you left it in, with no flash of the other state.
That also means it follows the browser rather than the person: sign in on a second machine and explain mode is off there until you press it. Clearing the site's local storage puts it back to off. It sets no cookie and sends nothing to the server.
Why it exists
The data pages are deliberately dense — a professional sheet, not a simplified one. The answer to a reader being put off by clean price and dirty price is not to thin the table out, but to keep the explanation one press away; explain mode is the version for a reader who wants all of the definitions at once rather than one at a time.
Where you will notice it most
The gilt lists, the post-tax table and each gilt's cash-flow schedule are the most annotated pages on the site, and the ladder page carries the bond ladder's seven terms on its mode links and form fields. Turn explain mode on before reading any of them for the first time and the page reads in order, from the labels outwards.
The terms it prints, and the two other ways to get at them, are set out in getting an explanation; the whole table on one page is the glossary. The terms this page draws on are the glossary's clean-price, dirty-price, accrued-interest, gross-yield, net-yield and index-ratio.