Method

How the sheets are made.

A sheet starts as a question people actually type: what size dehumidifier for a three-bedroom house, which battery does a Fiesta key take. If the honest answer is a number or a code, and that number or code can be worked out from documents anyone could read, it gets a sheet. If the honest answer is “it depends on taste”, it does not.

What counts as a source

The maker’s own manual, handbook or support page, first. A standards body, a regulator (Ofgem for the price cap) or a trade body second. A retailer’s page only when nothing better exists, and then the sheet says “seller” next to the row so you know to check the old part before you buy. A forum post, a video or another site’s table is never a source. Every source is linked at the foot of the sheet with the date it was read.

Rules of thumb

Some sheets use a rule of thumb (watts per cubic metre, lights per foot of tree) because that is how the trade works it out and no exact method exists for a room nobody has surveyed. The rule is named, its source is linked, and the sheet says what the rule assumes. If you have a surveyor’s figure, use the surveyor’s figure.

What software does and what a person does

The sums are code. The first drafts of the words, the search for documents and the checks that no row is missing its source are done with AI software; a person reads the documents, chooses the rows, and signs off every sheet. No sheet is published without a person having read the source for every row on it. Nothing is bought, tested or handled, and no sheet pretends otherwise.

When things change

Makers change part numbers, airlines change bag sizes, Ofgem changes the cap four times a year. Each sheet carries the date its data last changed. The Amazon listings linked from a sheet are checked nightly for whether they are still live; a dead one is swapped, and the search link under every button is there so the answer never dies with a listing.