Using The Correct Coiled Balance Spring

A home owner from Passaic Park,NJ says:
The coiled balance springs on the upper sash of one of my CertainTeed windows needs to be replaced. The number stamped on the spring is 335.

However, following the formula in your DIY guide, "Choose the Appropriate Coil Balance", the result calls for a 6 lb. spring (336 coil balance spring).

Which one should I use?
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Paul from SWISCO responded:
Thanks for posting! We always recommend that you order the original spring number the window manufacturer used, unless the spring was too weak to hold up the window sash.
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