Each nutritional component has a specified unit of measurement. When the notation "ppm" is used, the component is being measured in parts per million. Parts per million is also sometimes referred to as milligrams per kilogram, or mg/kg. Some components are measured in micrograms per kilogram, or mcg/kg or ug/kg. Micrograms per kilogram is equivalent to the notation "ppb" or parts per billion.
In some cases the old values for nutritional components have been changed. To prepare for this revision, information was obtained from a number of sources (including the National Research Council, personal conversations with prominent researchers in the field and others) and was then compiled for your quick reference.
When data on a particular nutrient was scarce or unavailable, the ingredients were assayed. Our computer system was then updated, using this information, and recalculated the chemical composition of all of our products. The reported figure on the nutritional composition of the diets is determined by calculating the level of each nutrient contributed by each of the ingredients using a computer matrix. These values are checked occasionally by an analytical laboratory. As a result, the information in this revised version is the most accurate, and current available.