How to determine sash-weight

A handy person from Woodbury, MN says:
October 3, 2017
I have a Milgard window with bad plastic pulleys, that pinch the cords in both of the 29" channel balance springs. I have ID'd the top and bottom plastic fittings on the balances from your photos, but I need assistance to determine the proper weight selection. Should I weigh the moveable single-hung window panel and divide the weight by two, half for each of the left and right balance, or do your part-numbers consider the full sash weight be applied for both balances?

Thanks,
Scott S
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Tom from SWISCO responded:
October 4, 2017
Measure the weight of the sash and compare it directly to the chart on the S390-29 webpage. The chart accounts for both balances, as well as friction supplied by the window frame. No math and no adjustments are needed.
29" Series 390 Channel Balance
29" Series 390 Channel Balance
S390-29
$11.10
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