Or

Author:
Cecil McIntosh

Focus on Accuracy and Precision, and how to calculate the Accuracy and Precision of measurements.

**Terms And Equations**

**Accuracy** – How close a measurement is to the actual or expected value.

**Precision** – How close a set of measurements are to one another.

**Error** – The difference between the actual or expected value, and the measured value.

**Absolute Error** = Actual value – Measured value

**Relative Error** = (Actual value – Measured value) / (Actual Value)

**% Error** – Relative Error X 100%

**Deviation** – The difference between a measurement within a set and the mean of that set of measurements.

**Deviation** = Measurement - Mean

**Average Deviation** - The average of the Deviations of all measurements within a set.

**Systematic Error** – Error that impacts all or a large portion of measurements in a set uniformly, or by some type of trend.

**Random Error** – Error that occurs sporadically, without any sort of trend or predictability.

**Offset error** – is when a machine is not calibrated or set to measure zero, when the sample is at zero.

**Multiplier error** - is an equipment malfunction where it amplifies changes in readings, or has a diminished sensitivity to change.

Source: Chemistry Quick Review of Experimental Error. Anne Marie Helmenstine, Ph.D., About.com,http://chemistry.about.com/od/chemistryquickreview/a/experror.htm.