Recalibrate a small weight scale by cleaning it, placing it on a flat surface and pressing the zero/tare button. Find the calibration weight for the scale in its manual or on the machine itself, press the calibrate button, apply the appropriate weight, and wait for the scale to blink, indicating it has finished calibration.
When cleaning the scale, use water and then a mild acid, such as rubbing alcohol, to ensure that small matter that could alter the scale's displayed weight is removed.
Finding the calibration weight can be challenging without the correct documentation. If the documentation cannot be found, contact the manufacturer or visit its website to find the appropriate calibration weight.
If measured weights are not available, nickels are a good substitution. Nickels weigh 5 grams each, so they may be used to make a rough calibration. Ensure the weights are clean so they give an accurate reading, and that the entire volume of weight is placed quickly, as some scales may timeout while waiting for the rest of the weight and calibrate incorrectly.
To check that the calibration was successful, turn the machine off and wait for about a minute. Turn the scale back on and weigh something with a known weight. If the scale displays a weight outside of its listed margin of error, calibrate it again from the beginning.