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• The base quantities of the SI system are length, time, mass, current, temperature, lumious intensity and amount of substance. Their definition is internationally uniform.
  • Definition of the units
  • Definition of all SI units (detailed)
  • History of the definition of length
    
• To avoid unwieldy multi-digit numeric values when specifying, for example, a length, the base unit is given prefixes, in this case "meter". This gives easy-to-handle numeric values of, in most cases, no more than four decimal places.
  • Prefixes for units
    
• In addition to the SI unit "meter", the direction must usually also be specified in length metrology. This is done via the angle. The angle is measured in degrees (°), minutes (') and seconds ('').
  • Angle definition
    
• Tip: If in mechanical engineering no unit is given when specifying the length, it is usually millimeters (mm).