Measurement is the process of determining the amount, level, or degree of something. There are many different types of measurements, including: length, width, height, depth, weight, area, volume, speed, temperature, pressure, density, energy and time. Measurements are made using a variety of tools and instruments.
The SI system (International System of Units) is the most widely used measurement system in the world. The SI system defines seven base units: meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol) and candela (cd). These units are used to measure everything from length and mass to electric current and luminous intensity.
In addition to the SI units there are many other units of measurement that are used in specific circumstances or for particular purposes. For example:
-The astronomical unit (AU) is used to measure distances between celestial bodies;
-The nautical mile (nm) is used for maritime navigation;
-The knot is a unit of speed equal to one nautical mile per hour;
-The bar is a unit of pressure equal to 100 kilopascals;
-The pound sterling (£) is the official currency of the United Kingdom;
-The gallon is a unit of volume often used in the US for measuring liquid volumes.