Technical Abstract: This paper is Part 1 of the Series of articles on Nutritional Metrology: The Science of Nutritional Measurements. A fundamental aspect of measurement is that all measurements have two parts: the measurement value and its uncertainty. Measurements are made to communicate information on properties of materials to serve useful goals. By definition a measurement is accurate when it is both precise and free of systematic error. Precision is an expression, the repeatability of a measurement. Measurements can have high precision yet still be in error. Food testing measurements communicate information on properties of food. For any request for measurements it is beneficial to ask, How good do the measurements need to be for purposes of the intended use of the data. A 1% uncertainty may cost an order of magnitude more than a 10% uncertainty.