Notes
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Where the √3 comes from in three-phase power Three phases 120 degrees apart do not add to three times one. The factor is 1.732, and it is geometry rather than convention. Per cent and percentage points are not the same thing A rate moving from 4% to 5% rose by one point and by twenty-five per cent. Both are true and they are not interchangeable. Ads, and where they are not Why nothing sits above the tool, and what that costs. A real coin is not quite fair A flipped coin lands the way it started about 51% of the time. The bias is in the physics, not the metal. The two-by-four is not two by four Some measurements are names rather than dimensions. Converting them gives an exact answer to the wrong question. The ten per cent you will cut off Every tiled or planked surface needs more material than its area. Where that allowance goes, and when ten is not enough. The year your money starts earning more than you put in There are two crossover points in a savings plan, twelve years apart, and only one of them feels like anything. 23 kg or 50 lb: the two numbers airlines weigh you against They are not the same limit. One is 2 kg more generous than the other, and which one applies depends on the ticket, not the airport. Series, parallel, and the two dividers that follow Two rules for combining resistors, and the dividers that fall out of them. Including the one where the formula swaps ends. When two cycles line up again Buses every 12 and 18 minutes meet every 36. The lowest common multiple is a scheduling tool before it is a maths exercise. Ordering by the cubic yard when it is sold by the tonne Gravel is used by volume and sold by weight. A loose heap is about 40% air, and that is where the order goes wrong. What to tip, by country The percentage is the easy part. Whether a tip is expected, insulting or already on the bill is the part that varies.
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