Why these three
They share a property that makes a calculator worth building: the answer is not obvious and a wrong answer costs something. Misjudging tax equivalent yield makes you reject a better bond. Misjudging RAID 10 fault tolerance makes you design an array that fails when a second drive goes. Misjudging surface speed burns an edge in twenty minutes.
Each page follows the same structure — the tool first, the formula next, then the assumptions, then the cases where the number misleads. If a calculator cannot explain when it is wrong, it is not finished.
What you will not find here
No accounts, no email capture, no "premium" lock on the result, and no sponsored rankings. The pages are static and run entirely in your browser — the numbers you type are never sent anywhere.
Coverage
The site is deliberately small. Rather than a thousand thin pages, there are three tools that are meant to be complete for the problem they address. More will be added when they meet the same bar, not before.