Two concepts that have to due with measurements are accuracy and precision. The accuracy of the measurement refers to how close the measured value is to the true or accepted value. For example, if you used a balance to find the mass of a known standard 100.00 g mass, and you got a reading of 78.55 g, your measurement would not be very accurate. One important distinction between accuracy and precision is that accuracy can be determined by only one measurement, while precision can only be determined with multiple measurements.
Precision refers to how close together a group of measurement actually are to each other.
Precision has nothing to due with the true or accepted value of a measurement, so it is quite possible to be very precise and totally inaccurate. In many cases, when precision is high and accuracy is low, the fault can lie with the instrument. If a balance or a thermometer is not working correctly, they might consistently give inaccurate answers, resulting in high precision and low accuracy. A dartboard analogy is often used to help students understand the difference between accuracy and precision. Imagine a person throwing darts, trying to hit the bullseye.