The following excerpt is from the November 12, 1892, edition of “Golden Days” magazine. It explains how condensed milk was made.

The process is simple; the fresh milk is put in an excellent great copper tank with a steam jacket. It is heated, and s and sugar is added. The mixture is then moved into a vacuum tank, where evaporate produces evaporation. The vacuum tank will hold approximately nine thousand quarts. It has a glass window at the top, through which the operator in charge monitors it. He can tell by the appearance of the milk when to shut off the steam. This must be done just now, or they will be spoiled.

Next, the condensed milk is drawn into forty-quart cans and set in icy spring water to revolve rapidly by a mechanism so that the contents cool evenly.

Ice is put into the milk to bring it down to the proper temperature if it is not cold enough. Finally, the market market-sedans are filled with milk by a machine that pours exactly sixteen ounces of milk. Workers place the spout while another worker removes them once they are filled.

Which of the following would be most helpful for the reader to understand the process of making condensed milk?