First of all, you need to remember that bakeries like to do everything by weight. This creates for a much more accurate product, since there are so many deviations with volume. A cup of flour will weigh differently, depending on whether the flour was sifted into the cup, scooped into the cup, packed into the cup, etc. But a pound of flour is always a pound of flour.
Speaking of flour, since it is the most common ingredient in a bakery, it is also the baseline of a baking formula. Each ingredient is given a percentage value. These percentages don't all add up to 100%. In fact, one ingredient will always be equal to 100%. If flour is present, then it is 100%. If there are multiple types of flour, the total weight of all flour is 100%. The percentage of the other ingredients is based on their weight compared to the flour:
The following list of ingredients:
8 oz/wt butter
16 oz/wt flour
20 oz/wt water
...would result in the following formula:
...because there is half as much butter as flour, and 25% more water than flour. If you had five pounds of flour, the formula would look like this:
2 lbs 8 oz butter
5 lbs flour
6 lbs 4 oz water
This makes it easy to scale recipes to any yield. Of course, as soon as you start adding anything to the formular that isn't weight-based (like number of eggs, or teaspoons of vanilla extract), the complexity goes up. Fortunately, any ingredient can be weighed, so it's easy to convert a recipe to a baking formula.
One more note: if any ingredient other than flour is used as the baseline (such as when flour isn't present in the recipe), it should be noted at the top of the recipe which ingredient is now 100%.