calculate

# File activesupport/lib/active_support/duration.rb, line 98
        def calculate(op, other)
          if Scalar === other
            Scalar.new(value.public_send(op, other.value))
          elsif Numeric === other
            Scalar.new(value.public_send(op, other))
          else
            raise_type_error(other)
          end
        end