# File app/models/period.rb, line 228
  def projection_data(observed_todo_data)
    if observed_todo_data.length <= 1
      velocity = party.current_speed
    else
      velocity = (observed_todo_data[0] - observed_todo_data[-1]).to_f / (observed_todo_data.length-1)
    end
    projection_data = dates.map do |date|
      if date < Date.today 
        nil
      else
        value = observed_todo_data[0] - (date-start_on+1).to_f*velocity
        value >= 0 ? value : 0
      end
    end
  end