Measurement is integral to physics and all scientific subjects. Kids compare attributes like height and toy amounts before learning math, showing measurement is innate. The International System of Units defines seven base units including the meter, kilogram, and second. The standard meter is defined as a specific number of wavelengths of orange-red light in a vacuum. The standard kilogram is a platinum-iridium cylinder kept by the International Bureau of Weights and Measures. The second is defined as a specific number of periods of radiation from a cesium atom.