Chemistry is a precise laboratory science, and the equipment of a chemical laboratory is usually involved with measurement. Balances are used to measure mass, pipettes and burettes to measure volume, and thermometers to measure temperature changes. Advances in electronics and computer technology have enabled the development of scientific instruments that determine the chemical properties, structure, and content of substances accurately and precisely. Most modern chemical instrumentation has three primary components; a source of energy, a sample compartment within which a substance is subjected to the energy, and some sort of detector to determine the effect of the energy on the sample. An X-ray diffractometer, for instance, enables the chemist to determine the arrangement of atoms, ions, and molecules that constitute crystals by means of scattering X-rays. Most modern laboratories contain ultraviolet, visible, and infrared spectrophotometers, which use light of various wavelengths