Accuracy & Precision
They are not the same thing. Accuracy refers to how close a measurement is to the accepted (correct) value. Precision refers to how close (or consistent) measurements are to one another. Accuracy refers to one measurement. Precision refers to multiple measurements. For example, look at the following images:
Bullseye 1
Bullseye 2
To determine the accuracy of an experiment, percent error is used. The formula for percent error is: PE = |(accepted-experimental) / accepted| * 100 Accepted values are known; experimental values have been calculated in laboratory. Precision is determined via the use of significant figures.
Bullseye 1
Bullseye 2
To determine the accuracy of an experiment, percent error is used. The formula for percent error is: PE = |(accepted-experimental) / accepted| * 100 Accepted values are known; experimental values have been calculated in laboratory. Precision is determined via the use of significant figures.
Numbers in Science
The above title links to some videos regarding how to regard significant figures.
IMPORTANT TO REMEMBER WHEN DEALING WITH SIG FIGS IN CALCULATIONS:
The calculated area must be rounded to make it consistent with the measurements from which it was calculated. An answer cannot be more precise than the least precise measurement from which it was calculated.
IMPORTANT TO REMEMBER WHEN DEALING WITH SIG FIGS IN CALCULATIONS:
The calculated area must be rounded to make it consistent with the measurements from which it was calculated. An answer cannot be more precise than the least precise measurement from which it was calculated.
Uncertainty in Measurement
Uncertainty of measurement is the doubt that exists about the result of a measurement. There is always a margin of error for any instrument. Usually, the margin of error is expressed as +/-, which provides a range that the actual measurement falls within. Laboratory glassware usually lists the uncertainty directly on the instrument. But just in case, the uncertainty of analog instruments (such as graduated cylinders & burets) is +/- half of the smallest division. The uncertainty of digital instruments (electronic balances, timers & thermometers) is +/- the smallest scale division.
Example: A stick that is 30 centimeters with an uncertainty of +/- 1cm means that the stick is actually between 29 and 31 centimeters long.
Example: A stick that is 30 centimeters with an uncertainty of +/- 1cm means that the stick is actually between 29 and 31 centimeters long.
Experimental Errors
Experimental error is the difference between the recorded value and the generally accepted value. Errors can be systematic or random. Systematic errors occur as a result of poor experimental design or procedure. An example of systematic error is reading the meniscus in a graduated cylinder incorrectly, using too much liquid in titration, and incorrectly zeroing an electronic balance. The only way systematic errors can be reduced is by careful experimental design.
Random errors are caused by the readability of an instrument, environmental changes and effects (such as room temperature), insufficient data, and human error. Random error can be reduced by experiment replication or repeatability.
NOTE: Don't confuse error and uncertainty. Error is the difference between obtained results and the actual accepted value. Uncertainty is the doubt regarding the measurement obtained.
Random errors are caused by the readability of an instrument, environmental changes and effects (such as room temperature), insufficient data, and human error. Random error can be reduced by experiment replication or repeatability.
NOTE: Don't confuse error and uncertainty. Error is the difference between obtained results and the actual accepted value. Uncertainty is the doubt regarding the measurement obtained.