Guides
10 in-depth explanations of the formulas, standards and trade-offs behind the tools on this site — written for this site, not paraphrased from somewhere else, with worked examples and sources where a claim needs one.
Finance
- Margin vs Markup: What They Actually MeasureTwo numbers, the same profit, and one very common pricing mistake.
- How Mortgage Amortization WorksThe same payment every month, but a completely different split between interest and capital.
- How Loan Fees Change the Real Cost of BorrowingThe advertised rate and the real cost of a loan are rarely the same number once fees are counted.
- Compound Interest, Explained With NumbersThe slow, unglamorous first decade is what makes the second one work.
Technology
- How to Calculate the Real Cost of a SaaS SubscriptionThe number on the invoice and the number that determines whether the software was worth buying are usually different.
- Cloud Costs vs Total Cost of Ownership: What Each Model MissesA monthly cloud estimate and a five-year build-vs-buy comparison are answering two different questions — mixing them up produces the wrong one.
Developer
- How QR Code Error Correction WorksA QR code can lose a real chunk of itself and still scan — here's the mechanism that makes that possible, and the trade-off it costs.
- JSON Formatting vs JSON ValidationPretty-printed JSON and valid JSON are two different claims — one is about how it looks, the other about whether it's correct.