What is weighing? Weighing is comparing a weight that we do know, to something which weight we do not know.

Nails (the kind used for building houses) are sold by weight. In two different ways, they are sold by weight. First, the size of nail is stated in terms of "pennyweight." For example, those big nails that are about three inches long and have heads on them are called "sixteen penny nails" because one nail weighs the same as sixteen pennies.

Secondly, they are sold by the pound. (If you were going to build a large house, you may need 100 pounds of those nails for the big boards that keep the house from falling down.) A fifty-pound box of 16-penny nails is about the same size as a gallon of ice cream!

So if we get a nail, we can put it on one side of the balance scale, and start putting pennies onto the other side, to see how much pennyweight the nail is.

The Bureau of Weights and Measures is a government agency that tries to make sure that people who sell things by weight are not cheating anybody. The Bureau (pronounced "BEW-row") has sets of "weights" that are made of steel, and they weigh exactly what the labels on them say they do. People from the Bureau go around to stores, and other places that use scales, put their weights on the scale, and see if the scale shows them the correct weight. If the scale shows that the Bureau's weight weighs more than it really does, that means that the store's scale is wrong and they may be cheating people by selling them a smaller amount of something than the
buyer thinks he or she is getting. The scale has to be fixed so it works properly. By using these very exact weights, proper adjustments can be made to the scale so it shows the correct weight.

So, when you buy something at the store that the clerk has to weigh in order to tell you the price, they are using their scale to compare a known weight (the Bureau's weight) to an unknown weight. That is, the Bureau's one-pound weight is known, and that is what the scale has recorded. When the clerk puts a chunk of hamburger onto the scale, and keeps adding little bits of meat to the chunk until the scale reads "one pound," the clerk is comparing the known weight to the unknown weight.