**Percent deviation is a number calculated to determine the accuracy of data collected during an experiment compared to the theoretically expected results.** Percent deviation is often used in student experiments to check for data errors.

Percent deviation is calculated by first subtracting the theoretically expected results from the actual data collected to get the deviation. That number is then divided by the theoretically expected results and multiplied by 100 to create a percent. A negative percent deviation shows that the measured number is lower than the theoretical value. A positive percent deviation means that the measured number is higher. A percent deviation lower than one correlates with accurate results and careful measurements.