Precision, Accuracy, and Error

Precision

Closeness of repeated measurements to each other; expressed as percent deviation.

Absolute Deviation

Difference between an individual measurement and the mean value.

Percent Deviation

Average absolute deviation divided by mean value, multiplied by 100; quantifies precision.

Accuracy

Closeness of measured value to the true or accepted value; expressed as percent error.

Absolute Error

Difference between measured value and accepted or true value.

Percent Error

Absolute difference between true value and experimental mean divided by true value, multiplied by 100; quantifies accuracy.

Parallax Error

Error caused by viewing a measurement scale from an angle rather than directly perpendicular to the meniscus or mark; produces incorrect readings due to apparent shift in position; avoided by placing eye level with the measurement mark.