Balance length question

A home owner from USA says:
Have Home Depot American Craftman Windows from 2006. Need balance springs. Looks like your 351 series. Metal measures 28" but numbers stamped on side are 27 4. Do I need 27" or 28"?
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Tom from SWISCO responded:
Don't worry, that's normal. If you have a stamp that reads "27 4," then the metal channel should be 28" long. I know it's confusing but that's just how the industry makes them.
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