So the apothecary took a small piece of sheet lead, rather thin, and cut off a little square of it. He then put it into one of his scale balances, and put a thin, square weight of brass, similar to it, into the other scale. The lead weight was a little too heavy. He then clipped off a very little with his scissors. This made it about right. Then, with the point of his scissors, he scratched a figure 1 upon it. “There,” said he, “boys, there is a standard for you.”
“What is a standard?” said Rollo, taking up the weight.
“Why, it is a weight made exactly correct, for you to keep, and make yours by. It is a one-grain weight. I will give you some sheet lead, and when you get home and have made your scales, you can cut off another piece, and weigh it by that, and so you will have two one-grain weights. Then you can put those two into one scale, and a piece of lead as big as both of them into the other scale, and when you have made it exactly as heavy as both of the others, you must mark a figure 2 upon it, and then you will have a two-grain weight. In the same way you can make a five-grain weight, and a ten-grain weight, and a pennyweight.”
“What is a pennyweight?” said Rollo.
“It is a weight as heavy as twenty-four grains.”
“The pennyweight will be very big, then,” said Rollo.
“Yes,” said the apothecary; “but you can take a little strip of lead like a ribbon, and then roll it up, when you have made it just heavy enough, and then it will not take up much room. So you can make another roll for two pennyweights, and another for five pennyweights, and another for ten pennyweights.”
“And another for twenty pennyweights,” said James.
“Yes; only twenty pennyweights make an ounce. So you will call that an ounce weight. But you cannot weigh more than an ounce, I should think, in your knitting-needle scales.”