Channel balance spring weight option

A quick learner from Jacksonvil says:
June 4, 2017
In looking at the examples of your channel balances, the 29" series 380 channel looks accurate when compared to mine. This includes the shoe, the top and the clip. However my stamp only reads 28.5 ks caldwell, so I really have no idea what this means in regard to what weight range to choose. Can you help?
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Tom from SWISCO responded:
June 6, 2017
A stamp of 28 5 usually corresponds to our 2850 option. You can always weigh your sash to be sure.
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29" Series 380 Channel Balance
S380-29
$11.10
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