Data and sources.

Every number this site publishes carries its origin, the date it was last checked, and one of three statuses. The distinction is not bureaucratic: a figure fixed by a standard, a figure read off a shelf last month, and a figure everybody repeats without a source are three different kinds of claim, and treating them alike is how calculators end up asserting folklore.

The three statuses

Standard

Set by a citable normative source — PS 20, TCNA, ANSI, ASTM. Quoted with its reference.

Market survey

Measured on products actually on sale, with the date and the sample size. It expires.

Convention

Widely repeated, no normative source. Presented as a convention, never as a rule.

The register

What expiry means here

A market survey carries an expiry date. When it passes, the value is removed from the pages that use it rather than left on screen with an old date attached. A price that was true a year ago, displayed today without saying so, is worse than no price.

What we deliberately do not publish

• Saw kerf. It belongs to your blade, not to a table. It is an input on every page that needs it, with a starting value you are told to replace.
• Material prices. Not yet. Publishing a price means committing to a sample size, a date and a refresh cycle. Until that is in place, the pages that would show one say so instead — as the wall paneling tool does.
• Brand product data we have not read ourselves. A page named after a retailer that does not carry that retailer's real roll widths, box coverages or panel sizes has no reason to exist.

The rounding rules and the limits of the geometry are on how we calculate.