You could just weigh a 4-ounce stick of butter (or a pound or a kilo) to see if the scale is in the ballpark. If it’s close enough, you may be satisfied — after all you’re a baker, not a rocket scientist, right? On the other hand, if you weigh small quantities, like salt and leavenings, or if you just believe that a tool should do what it’s supposed to do, read on.
You could use calibration weights (purchased online) to check your scale’s accuracy, or you can use ordinary pocket change.
Before testing your scale, you should check the year of your US pennies. These instructions work for the zinc pennies made after 1982. Before 1982, pennies were mostly copper and weighed about 3.1 grams. Pennies made in 1982 could be either type. Here’s a link to the US Mint page on coin specifications.
Canadian coins are lighter. A Canadian 5-cent coin weighs 3.95 grams since 2000. A Canadian 1-cent coin weights 2.35 grams since 2000. Before 2000, coin weights changed several times due to changes in metal content.
If you live in another country, check out your government mint web site or coin collectors web sites for gram weights of your local coins.