• Some measuring tools measure in both metric and Imperial units.steel ruler image by dwags from Fotolia.com
  
  The metric system of measurement was invented in France and used throughout Europe. Its basic units of measurement are for distance, weight, volume, temperature, time and electric current. All of its other units of measurement are actually different combinations of these basic units. There are a great variety of tools used for measuring with the metric system.
  
  

Metric Rulers and Tape Measures

• The simplest metric measuring device is the metric ruler. A metric ruler is a narrow straight length of wood, plastic or metal marked along its length with millimeter and centimeter units. Long metric rulers might also have a meter unit. Rulers measure distances. A metric tape measure is a long, flexible tape that rolls and unrolls to measure distances of many meters.
  
  

Metric Scales

• Metric scales measure weight in either grams or kilograms. There are three types of metric scales. Metric balance scales have two plates attached to a lever. On one side are placed known gram weights. The unknown sample is placed on the other. When the plates balance, the unknown weight is equal to the known weights. Metric spring scales have the unknown weight attached to a spring of known properties. The spring stretching moves a pointer to the gram or kilogram weight. Digital metric scales use electronic circuits to determine the weight of an unknown sample in grams or kilograms. Hydraulic and pneumatic metric scales are used for measuring very heavy objects. They use fluid pressure changes to determine weights in kilograms.
  
  

Metric Graduated Cylinders

• Metric graduated cylinders are used to measure volumes. They are essentially tall cylinders of glass or plastic with marks up their sides. The marks are in units of fractions of a liter, most often milliliters. The cylinder is partially filled with water and the volume of the water is read. An object of unknown volume is placed in the water and a new reading is taken. The first reading is subtracted from the second. This gives the volume of the object.
  
  

Celsius Thermometers

• The Celsius temperature scale is the scale used by the metric system. It is based on the freezing and boiling points of water. Thermometers marked in degrees Celsius are metric temperature measuring tools.
  
  

Watches and Clocks

• The second is the basic metric unit of time. Metric time units are shared by other measuring systems like the Imperial and U.S. systems. Watches and clocks are metric time-measuring tools.
  
  

Ammeters

• Ammeters are metric current-measuring tools. They consist of two metal contacts connected to sensitive electric circuits which are in turn connected to a gauge. The gauge's needle moves an amount that is proportionate to the electric current flowing in the circuit. An ammeter measures current in amperes.