My balance is stamped with 3130, but it weighs 28.5 pounds!

A quick learner from Roseville says:
I have a window that shows a 3130 bsi lm. However, I weighed myself with the window and it is coming in at 28.5 pounds. The metal part of the channel balance is 32" long. Is 3130 too light? Should I go to the 3150 or just under at 3140?

What does the lm stand for? I know I need the 385 ends based on the other window I replaced. But, since this is the same size window, the last owners messed all this up because I bought the wrong size from you on the other window.
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Thanks for posting! Since your sash is 28.5 pounds, I would recommend our 3150 option. I'm surprised this old balance was using the 3130 option. Did you ever find that it was difficult to operate?

I'm not sure what the "LM" stands for, but I assume it's some kind of manufacturing mark. I wouldn't worry about it.
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