Guides

The arithmetic and the reasoning behind the tools, with worked examples you can check against your own numbers.

• 13 Oct 2026How to remove VAT from a price, and why subtracting the percentage is wrongDivide by 1 plus the rate. Subtracting the percentage understates your net price by exactly the rate squared. The proof, a table and a worked example.
• 12 Oct 2026How robots.txt really works: which rule wins, and what it cannot doMost robots.txt mistakes come from reading the file like a firewall. It is a set of requests with three precise rules for resolving conflicts — and a few things it never does.
• 11 Oct 2026Why Google cuts your title by pixels, not charactersThe 60-character rule works for average text and fails at the extremes. Here is what a title actually costs in pixels, measured, and how to stay inside the line.
• 5 Oct 2026Hreflang mistakes that quietly break international targetingHreflang fails silently: a broken set looks fine on the page you check. Ten mistakes, a worked example, and a short script that finds the ones you cannot see.
• 4 Oct 2026ACOS to ROAS: how to convert, and the margin check that decides if you're profitableOne formula converts ACOS to ROAS and back. The number that tells you whether a campaign made money is a different one — your break-even.
• 4 Oct 2026How to calculate CPM: formula, worked examples and reverse mathsThe CPM formula, the two ways to rearrange it, and a full worked media plan that follows one budget all the way to cost per acquisition.