The first step in using a battery equivalent chart is finding the model number of the battery in question on the chart. All other battery models on the same row as the battery in question are equivalent to that battery.
Battery equivalent charts are mostly used to make sense of the many different models of watch batteries produced by different manufacturers. In addition to major battery manufacturers, watch manufacturers also produce batteries, often with different model numbers. The watch battery that Timex calls "D," for instance, is the exact same battery that Bulova calls "226." To add to the confusion, Energizer, Eveready and Rayovac call this same battery the "301" model, while Maxell, Panasonic and Sony call it the "SR43SW."
Knowing how to use a battery equivalent chart makes sense of this confusing system. If a watch owner knows the model number of the battery he has, then using the chart tells him all the other battery models to which that particular battery is identical. This is an advantage, as generic watch batteries are often more widely available and more affordable than batteries produced by the watch manufacturer.
Battery equivalent charts are largely restricted to watch batteries. The disposable batteries used in most other types of small electronic devices use a standardized system in which all manufacturers use the same name for every particular battery size, making equivalent charts unnecessary.