How do calculate percent error

Percent error is always positive, but step one still contains the error initially flagged by Mark. The answer in that step should be negative:. Mark is not correct. Percent error is always positive regardless of the values of the experimental and actual values. Please see my post to him. Say if you wanted to find acceleration caused by gravity, the accepted value would be the acceleration caused by gravity on earth 9. If you are performing a chemical reaction to quantify the amount of carbonic acid, the accepted value is the theoretical value if the reaction goes to completion.

If you are measuring the value using an instrument, you have uncertainty of the instrument e. Step Subtract one value from others to get the absolute value of error.

Step Divide the error by actual value. Example 2: Harry got a traffic penalty notice for police speeding for traveling 70 mph in a 60 mph zone. Harry claimed his speedometer said 60 mph, not 70 mph. What could Harry claim as his percent error? Harry can claim Example 3: Helen's math class had 24 students yesterday. She miscounted the class total and recorded it as 18 students. What is Helen's percent error? The actual number of students: 24 and Recorded number of students: Example 4: The Handbook of Chemistry and Physics lists the density of a certain liquid to be 0.

Daniel experimentally finds this liquid to have a density of 0. Prove your answer. Given, Theoretical value of density of a liquid: 0.

Daniel got a 0. But, the teacher allows only a 0. So, Daniel could not make an "A". If the experimental value is less than the accepted value, then the percent error is negative. Generally, the error is calculated as the absolute difference to avoid the confusion of a negative error. Percent error tells us how much extent few unavoidable errors affect our experimental results.

It is measured by taking the difference between the actual value and the observed value. Small percent errors indicate that you are close to the accepted or real value. Percent errors tell how big your errors are when you measure something in an experiment.

So, a high percent error is bad. By increasing accuracy, precision and taking the measurements under controlled conditions, we can decrease the percent error. Example: The report said the carpark held cars, but we counted only parking spaces. Example: Sam does an experiment to find how long it takes an apple to drop 2 meters. The theoretical value using physics formulas is 0. But Sam measures 0. Example: They forecast 20 mm of rain, but we really got 25 mm.

Example: You measure the plant to be 80 cm high to the nearest cm This means you could be up to 0. Percentage Difference Percentage Index.