Method · never monetised
How we source figures
Every number on this site is either sourced or visibly absent. There is deliberately no third state, because the third state (a plausible figure with no origin) is how a guess reaches a published page.
Sourced or absent, never estimated
Figures are held in code as one of exactly three things, and none of them is a guess.
- Sourced. A value carrying the source it came from and the date that source was checked.
- Absent. An instruction describing what still has to be found. It renders as not yet sourced: a visible gap, never a blank, never a dash, and never something that reads like a measurement.
- Placeholder. Where a table would not read at all without something in the cell, that cell shows XXX. Not an estimate, not a rounded figure, not a typical value, a mark meaning no figure exists yet.
The fourth state (a plausible-looking number with no origin) has no way to be written. A build check refuses to let a page be indexed, or submitted to a search engine, while it holds a single absent figure or a single XXX, and refuses to let a number reach a page by any route other than the first of the three above.
This is why you will sometimes see XXX where you expected a price. It means we have not measured it. It does not mean the price is small, or uncertain, or withheld.
What we will not do
- Restate a number from memory. A figure is only true of the source it came from, on the date it was retrieved. Sources are re-read at the point of quoting.
- Average a range into a single confident number. Where the honest answer is a spread, the page shows the spread and what moves it.
- Describe a sample we do not hold. If a page says a figure came from collected quotes, those quotes exist and their count is stated.
Certification: absence is not a negative
Our certification data covers NSF listings only. A brand with no NSF row means we did not find an NSF listing. It does not mean the product is uncertified. Products may be certified by WQA or IAPMO instead: WQA’s directory blocks automated access entirely, and IAPMO is not covered here at all.
Certification is granted per model, not per brand, and a product certified for one claim is not certified for the others. Wherever certification appears on this site it carries NSF’s own “current as of” date.
When we get it wrong
Corrections are published rather than quietly edited. Every figure we have changed since publishing it is listed on the corrections page, with what it was, what it is now, and why it moved.
How we make money
Some outbound product links earn a commission. That relationship is disclosed on every page carrying such a link and in full on the disclosure page. This page, the disclosure page and the corrections page carry no monetised links of any kind.