Accuracy and Precision

Accuracy and precision are important concepts, as they relate to any experimental measurement that you would make. Accuracy refers to how closely a measured value agrees with the correct value. Precision refers to how closely individual measurements agree with each other. In any measurement, the number of significant figures is critical. The number of significant figures is the number of digits believed to be correct by the person doing the measuring. It includes one estimated digit. For example, a scale can only mass an object up until a certain decimal place, because no machine is advanced enough to determine an infinite amount of digits. Machines are only able to determine a certain amount of digits precisely. These numbers that are determined precisely are called significant digits. So a scale that could only mass until 99.999 mg, could only measure up to 5 significant digits. In order to have accurate calculations, the end calculation should not have more significant digits than the original set of data. The easiest method to determine significant digits is done by first determining whether or not a number has a decimal point. This rule is known as the Atlantic-Pacific Rule. The rule states that if a decimal point is absent, then the zeroes on the Atlantic/right side are insignificant. If a decimal point is present, then the zeroes on the Pacific/left side are insignificant. The weight of gold, brought up in the “Atomic Weight Changed for 19 Elements” article , is being updated from 196.966 569(4) amu to 196.966 569(5) amu, where the numbers in parentheses represent the uncertainty in the last digit of the atomic weight.



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