A home owner from Ontario canada says:
August 4, 2016
Have a couple windows in house with broke springs. Took one out and got an image of the side stamp. Which one do I need off your site. Thanks
Paul from SWISCO responded:
August 8, 2016
I see you were looking at our Series 770 balance. Is that the same series as yours? I'm afraid the stamp does not confirm. If you do have the Series 770 then I would recommend measuring your metal channel to determine the correct length and weighing your sash on a scale to determine the best option.