Machines · what the machine is
A cavity and a magnetron
This is the category where the two headline figures stop separating anything. Most of the listings here state one identical pair, and the pair is the first thing on the box.
What the listings describe
A cavity stated in cubic feet. A wattage. A door, sometimes described by its mechanism. A turntable, described as removable in several listings and measured in inches in two of them. A control panel with some combination of counted presets, counted power levels, an eco mode, a mute button and a child safety lock.
This site describes the machine at that level and no further. It offers no account of what happens inside the cavity, because that would be this site explaining physics it has not been given a source for.
What the numbers attach to
The cavity figure attaches to the box. The wattage attaches to the machine as an input rating. The preset count and the power level count attach to the control panel, and both appear under several different names across this one category.
When most of a category states the same cavity and the same wattage, the counted figures on the control panel are all that is left to compare, and those are the figures with no definitions behind them.
What is regulated
Microwave ovens are regulated in the United States as radiation-emitting electronic products under a federal performance standard, published at Title 21 of the Code of Federal Regulations, part 1030. The Food and Drug Administration maintains a consumer page about that program. Both documents are linked below, and this site does not paraphrase either of them beyond saying that they exist and what they cover.
What does not change when the count changes
The cavity and the door. Most of the listings in this category state the same cavity figure as each other, which means the part that does not change between listings is also the part they all print largest.