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Calculators
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Blog
Blog
Short pieces on the arithmetic the calculators do, and the places it usually goes wrong.
Margin vs Markup: Why the Two Are Not the Same Number
The same dollar of profit, divided by two different numbers, gives two very different percentages.
Why a 50% Drop Needs a 100% Rise to Get Back
A 20 per cent fall followed by a 20 per cent rise does not return you to where you started.
Small Rate Differences, Large Amounts of Money
The difference between 6 and 6.5 per cent is not eight per cent more interest. Over decades it is far more than that.
What BMI Can and Cannot Tell You
A single number built from two measurements cannot distinguish muscle from fat, and was never designed to.
Unit Conversion Mistakes That Cost Real Money
The dangerous conversions are the ones where both units are called the same thing.