The publisher, John Wiley & Sons, offers RealTime Physics as a four module set covering the topics of mechanics, thermodynamics, electricity & magnetism and optics. We are only using selected labs out of these four books, so the publisher created a custom with just those labs. Therefore, you do not have to purchase four different books, just the custom edition. Since the custom edition is composite of the original four module set, there are some oddities. For instance, most pages have two page numbers. The page number at the very bottom is the page number in the custom edition, while the number above it is the page number in the original edition. Likewise, the lab numbers are based on the original edition. So our first lab has the title of Lab 2: Changing Motion. This is because it was the second lab in the mechanics module of the original edition. There are 13 labs listed in the table of contents, but we will only do 12 labs. That is because Lab 9: Magnetism and Lab 10: Electromagnetism will be treated as one lab. You will only need to complete certain items in both labs, and you will be given a list of these items in advance.