tilt window block & tackle balance

A quick learner says:
I have a tilt window with a plain channel and looks very much like the 765 series. It is 21 inches long and on the channel it says w 20 3 ex cmcl. From that info my guess was I should order the 20-3 option and just want to confirm if that is correct.
Thanks
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Paul from SWISCO responded:
Yes, a stamp of 20 3 corresponds to our 20-3 option.
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