Accuracy: Hitting the Target
Accuracy describes how close a measurement is to the true value. A scale that reads 100.0 g when you place a 100 g weight on it is accurate.
Precision: Repeating the Result
Precision describes how consistently repeated measurements cluster together. A scale that reads 99.2 g every single time is precise but not accurate. A scale that gives a different number each time is neither precise nor accurate.
Why Both Matter in Conversion
A converter uses exact factors, so it preserves whatever precision the input had. If your input measurement is imprecise, the converted output will be equally imprecise — the calculator can't add accuracy that wasn't there. Understand the source of your number before trusting many decimal places of output.