text: A quantity equation, also sometimes called a complete equation, is an equation that remains valid independently of the unit of measurement used when expressing the physical quantities.
  In contrast, in a numerical-value equation, just the numerical values of the quantities occur, without units. Therefore, it is only valid when each numerical values is referenced to a specific unit.
  For example, a quantity equation for displacement  as speed  multiplied by time difference  would be:
  for  = 5 m/s, where  and  may be expressed in any units, converted if necessary.
  In contrast, a corresponding numerical-value equation would be:
  where  is the numeric value of  when expressed in seconds and  is the numeric value of  when expressed in metres.
  Generally, the use of numerical-value equations is discouraged.