Guides

Math guides

Most of the math a programmer meets arrives disguised as a bug. These guides work through the ideas visually, starting from the code that made them matter.

Numbers

Why 0.1 + 0.2 is not 0.3
Every language gets this answer, and it is not a bug. Binary floating point cannot hold 0.1, so the number you typed was never the number that got stored. Here is what is actually in there, and what to do about money.
Beginner·11 min·2026-09-08

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Math guides

Numbers

Why 0.1 + 0.2 is not 0.3

Built in public.