Students often assume that each measurement that they make in the laboratory is true and accurate. Likewise, they often assume that the values that they derive through experimentation are very accurate. However, sources of error often prevent students from being as accurate as they would like. Percent error calculations are used to determine how close to the theoretical values, or how accurate, their experimental values really are.

The value that the student comes up with is usually called the **Experimental value**, or the experimental value. A value that can be found in reference tables is usually called the **theoretical value**, or the accepted value. The **percent error **can be determined when the **theoretical value** is compared to the **Experimental value** according to the equation below: