gistfile1.rb

class InvoicePresenter < BasePresenter
  def shipping_total(period_start, period_end)
    company.invoices.for_period(period_start, period_end ).one_off.sum(:total)
  end
end

and then in your view

presenter.shipping_total("11-1-13", "12-1-13") 

this really cleans up your view logic but allows you acccess to the scopes that your controller has