def deviation( inputValues )
      raise "'inputValues' must not be nil" if inputValues.nil?
      raise "'inputValues' must be an Array" if not inputValues.is_a?(Array)
      raise "'inputValues' must have at least two elements" if inputValues.length < 2
      value = inputValues[0].to_f - inputValues[1].to_f
      value.abs
   end
def deviation( inputValues )
      raise "'inputValues' must not be nil" if inputValues.nil?
      raise "'inputValues' must be an Array" if not inputValues.is_a?(Array)
      raise "'inputValues' must have at least two elements" if inputValues.length < 2
      value = inputValues[0].to_f - inputValues[1].to_f
      value.abs
   end
Given an array of two numbers, return the difference between the numbers as a positive number.