Things You'll Need
Gram scales help you weigh things by the gram, the base unit of measurement in the metric system. The most common models are digital and small enough to fit in your pocket. If the batteries have died in your gram scale, the scale itself has broken, or you do not have a gram scale to begin with, improvise one from things around your house. It may not be digital or fit in your pocket, but this scale will get the job done in a pinch.
Tie the string around the center of the yardstick, where it says 18 inches, then secure it with a piece of tape on either side of the yardstick. This keeps the string from sliding down the yardstick.
Seal a business envelope and fold it perfectly in half, lengthwise. Cut the envelope in half along the crease created by the fold. Tape one envelope half to each end of the yardstick.
Suspend the scale by the string somewhere where it hangs freely and you have a clear view of both it and something you know is horizontal, such as a window sill or door frame. It must hang from something static; if you hold it, the slightest movement of your hand will cause inaccurate measurements.
Line yourself up so that the yardstick is between yourself and the known horizontal object. Examine the empty scales and make sure the yardstick hangs parallel with the horizontal object.
Add a small piece of tape to the envelope on the higher side of the scale if it does not hang horizontally. Continue adding pieces of tape until the yardstick hangs true to horizontal.
Put a one-gram weight or something known to weigh one gram, such as a crisp dollar bill, in one of the envelopes. When you add something to the other side, that side will hang low if the item weighs more than a gram, high if it weighs less, and perfectly level with the other end when the object weighs one gram.
Use other items with known weights to measure multiple grams. For instance, use a nickel on one side of the scale for five grams.