Generally any measuring device needs to be calibrated to be useful. Calibration is the process where the measuring device is compared to standard units. Standard units are of value because they are also understood and used by other people. The most useful units are those used worldwide. If you are not familiar with the System International, often abbreviated SI, read details about those standard units.
The SI unit for mass is the kilogram. One liter (roughly one quart) of water has the mass of one kilogram (abbreviated kg). If that is too large a unit, the gram is 1/1000 as large.
You may borrow or purchase a set of masses that have already been calibrated. If you purchase a balance, it generally will have been calibrated by the manufacture. If you use a computer-based balance, the software likely includes a calibration file. So why learn about calibration? Measuring instruments, like musical instruments, get out of tune and needs to have their calibration checked or revised periodically. Depending on the balance you plan to use, the procedure varies: a student-made balance, a purchased mechanical balance, or an electronic balance.
Describe your calibration efforts and experiences in your science journal. Write a Formal Report if you need to earn credit.
Check the calibration of the balance when you first use a balance and periodically thereafter, depending on the importance of the accuracy of your measurements. To do that, you will need to borrow, purchase, or find a primary standard. It may be easiest to search the kitchen or grocery store for several appropriate sized packages which you have some confidence are close to their labelled masses. Use the balance to weigh the packages pretending you don't known the labelled masses to avoid prejudice. The calibration should be checked over the range of the balance from nearly zero to the maximum.
Record your calibration results in your science journal and write a Formal Report if you need to earn credit.
Inexpensive electronic balances generally do not actually measure mass, but rather an electrical signal which depends on gravitational force. The balance's calibration is stored as a small computer file listing the electrical signal and the correlated mass. Check the calibration of the balance when you first use an electronic balance and periodically thereafter, depending on the importance of the accuracy of your measurements, and make a new calibration file if needed. To do that, you will need to borrow or purchase a primary standard. It may be easiest to search the kitchen or grocery store for several appropriate sized packages which you have some confidence are close to their labelled masses. Using the existing calibration file, weigh the packages pretending you don't known the labelled masses to avoid prejudice. The calibration should be checked over the range of the balance from nearly zero to the maximum. If your measured masses are significantly different from the standards and you have confidence that your primary standards are accurate, create a new calibration file using the directions provided by the manufacture.
Record your calibration results in your science journal and write a Formal Report if you need to earn credit.