Formelsamling.se
Every page works through an example and names the mistakes that are easy to make with that formula. Swedish upper secondary maths, physics and chemistry.
What it is
Formelsamling.se is written in Swedish and published only in Swedish. There is no English edition.
It holds 237 formula pages for Swedish upper secondary school: 137 in mathematics and 100 in physics and chemistry. One page per formula, and no login.
Getting the claims right
At that size the risk is not the formulas. It is the claims around them, which can be wrong without looking wrong.
Two of those claims are checkable facts. Which course does a formula belong to, and does it appear on the official crib sheet handed out with the national test? Both are things a reference can assert from memory and be wrong about. Course placement is not taken on trust: each formula is checked against Skolverket’s official syllabus API, which is free, needs no key and is CC0 licensed. Each formula also records which national-test crib sheet actually carries it, and that field is left empty when the answer is none.
The other risk is authority. The site is written by one person whose degree is in electrical engineering, not in teaching.
The author is credited with one qualification, Civilingenjör i elektroteknik from KTH, and the site says in plain Swedish that he holds no teaching certification and has no teaching experience. An automated test asserts that the site’s structured data never implies otherwise. The site does not claim to be teacher-reviewed.
How it is built
The site is a static Astro build. Every formula page is a Markdown file a person wrote.
Two gates run before anything is published. Every formula’s LaTeX has to parse in KaTeX strict mode or the build fails. A content lint rejects broken LaTeX, a related link that points at nothing, and a formula claimed to sit on a national-test sheet that does not exist.
Diagrams are hand-written SVG, rendered at build time from a closed set of figure kinds declared in each formula’s front matter. Two JavaScript charting libraries were measured first. Mafs added 149.9 kB of gzipped JavaScript and put no figure in the static HTML at all; JSXGraph added 247.7 kB and also produced nothing static. The SVG route adds 4.2 kB of JavaScript and ships 2,035 bytes of real figure in the HTML that is served.
What is derived rather than typed in happens at build time. A box plot’s quartiles, a scatter plot’s regression line and a graph figure’s node degrees are computed from the underlying data, so a diagram cannot drift out of step with the numbers beside it.
The unit hub at /enheter/ is built the same way. The hub works out which courses and which formulas use each unit from the site’s own content, and it holds the outbound links to the per-unit pages on Konvertera.nu.
Built with astro