Some individuals and small business people need to use accurate gram scales in the course of business. For example, if you're buying or selling jewelry for its gold or silver content, you'll need an accurate measure of the gold or silver content in order to know that the deal is fair. But a gram scale which is not calibrated is useless. Here we will explain how to calibrate a gram scale, and point out some tempting shortcuts to avoid.
Gather your materials, most notably the calibration weights. You may have heard that so many quarters or other coins equal so many grams, and be tempted to use pocket change as your calibration weights. Don't make that mistake. Coins are not calibration weights. They vary in weight more than calibration weights, even at the time of manufacture. Furthermore, coins can be worn--reducing their weight. And they can be dirty--increasing their weight. Use only calibration weights. It's best to buy your own and keep them, so that you can recalibrate your gram scale often. It's not a one-time thing--recalibration needs to be done when the temperature changes more than a few degrees, for example. Some manufacturers recommend recalibrating after 10 hours of scale use (see Resources below).
Let your gram scale's temperature change to room temperature. Although it's probably already at room temperature, this is an important step that should not be overlooked. A gram scale that is too cold or too hot can't be accurately calibrated.
Second, place your gram scale on a hard, clean, flat surface and turn it on. Because electronic gram scales vary in design, screen feedback, and operation, you should refer to the user's manual of your model to understand the scale's communication with you. Select the calibration function. It might be a button on the scale, or a selection from an internal menu.
When you select the calibration function for your scale, your scale will guide you through a short series of steps. The order and number will depend upon your scale's model and design. It might ask for a "0" reading first. You make sure there's nothing on the scale and select "next." The scale may then ask for a 100 g weight. You place the 100 g weight on the scale, allow it to read the weight, and--if necessary--select next. Some scales proceed to the next step automatically; some scales require that you do it. Your scale's screen, together with a "translation" of its symbols if necessary in your user's manual, will guide you through the process of calibrating the scale. Some scales require only a zero weight and a weight at the other end--say, 500 g. Others require more data points: zero, 100 g, 200 g and 500 g, for example. Many scales ask you only for a single datapoint (100 g, for example).
When you've finished stepping through the scale's calibration procedure, you're finished, except for one not-so-obvious step: leave your scale where it is. If you move it to a room with a different temperature, or if you handle it roughly or carry it around in your car, the calibration will no longer necessarily be accurate. And in fact it will probably be inaccurate in those cases.