When a force acts upon an object it can cause the object to be pushed, pulled, accelerated, or deformed. In physics a force has both a magnitude and a direction. One common measurement is the Newton. In 1678, Robert Hook discovered that the distance a spring stretches is proportional to the force applied to the spring. Hooke's law is the reason why springs are common to use in force meters. A basic force meter can be created and calibrated very easily.
Cut the cardboard into a rectangle shape. The piece should be small enough to easily lift by hand but long enough for the elastic band or string to stretch when weights are attached to the meter.
Attach the elastic band or spring near the top of the cardboard using tape or staples. Test the band or spring by pulling gently on it to make sure that it is securely attached.
Reshape a paper clip into a S shape. Wrap one of the ends of the S around bottom of band or spring and attach firmly. Test by pulling slightly on the apparatus again to make sure everything holds.
Place a small mark on the cardboard where the band and paper clip join together. This should be marked as 0 N which stands for zero Newtons. This is where the entire apparatus is balanced with no additional force in weight acting upon it.
Calibrate the force meter by standing it vertically and attaching weights to the end of the paper clip. Use a 100 gram weight to determine where 1 N, or 1 Newton is located. Mark the cardboard. The mark should be placed where the band or spring meets the paper clip. Use weighted amounts of 200 grams for 2 N and 300 grams for 3 N and mark each on the cardboard.