| We express
        the distance in kilometres when it is large, such as the distance between
        two towns. We express
        the distance in millimetres when it is small, such as the thickness of
        a pencil.
 The same measurement
        can be expressed in any unit but we have to use the most suitable unit.
        Besides, we sometimes have to add or subtract several measurements. In order to do this, they have to be expressed in the same unit, that is why it is fundamental to know how to convert units.
 | 
  
    |  | The series
        of length units work in the same way as the units of our numeration system.Each
        unit has a value ten times larger than the unit on the right and ten times
        smaller than the unit on the left.
 You
        have to notice in which direction the unit jumps in order to move the
      decimal point in the same way.
 
        
          | This
              activity shows a measurement expressed in a certain unit and on
              the right you will find the unit to do the conversion.Type
              the resulting number in the small window below.
 After
              typing the number hit Enter.
 If
              your answer is correct, this number will appear. If it isn't, try
              again.
 |  
      When you click
      on Init, a different activity will appear. Do several conversions until you master unit
      conversion. |