Error is a negative word and when we say "error in measurement", we think that the person who measured has made an error because he did not fulfill his responsibility properly. It's not that the measurement can sometimes cause errors due to negligence but we need to know that the instruments we use to measure are never accurate. So there is a limit to how accurate it is to measure, that is, it is normal to have errors in measurement, but there must also be a measure of how accurate the measurement is. Therefore, the accuracy of the results can be greatly enhanced by the fact that the results of a test can be accurately reported . A measure of the accuracy of the test results can be given by knowing some common rules to find out the accuracy of the test results.