Ask anyone what a kilogram is in pounds and you will hear 2.2. It is a fine answer for a bag of flour and a wrong one for anything that gets multiplied. The real figure is 2.20462262, because a pound is defined as exactly 0.45359237 kilograms — a definition fixed by international agreement in 1959 and unchanged since.
The difference looks harmless: 0.2%. Then someone converts a 24-tonne container load with the short figure and books freight for 52,800 lb instead of 52,911 lb. The error is 111 pounds — an entire passenger worth of weight that exists on the scale and not on the paperwork.
Round last, always
The rule every converter here follows: carry the full-precision factor through the arithmetic and round once, at display time, to the precision the reader asked for. Rounding the factor first and then multiplying bakes the error into every result, and it compounds when conversions chain — kg to lb to stone, each step rounding again.
This is also why the reference table on the conversion pages shows five decimal places. Not because anyone weighs flour that precisely, but so the number you copy is the number the definition gives — and any rounding that happens after that is yours, made once, on purpose.