Stamp Number match

A home owner from Bel Air, MD says:
my window balance has the number 30 3 Caldwell AM printed on it. I am ordering 4 of the 31" series 380, would I need to select the option 3030 for the correct fit?

Thanks for the help,
User submitted photo of Caldwell channel balance.
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Donna from SWISCO responded:
Good Afternoon,

Please take a look at the Swisco Series 380-31" Channel Balance with the stamp option 3030. The 3030 stamp will carry an approximate sash weight range of 16 through 13 lbs. If you want to confirm the correct stamp option, remove the window sash and place it on a scale to gather its weight.

*This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
A quick learner says:
The sash is 20 pounds.
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Donna from SWISCO responded:
Hi Tony,
Sorry for the typo above. The 3030 stamp option will carry a window sash weight range of 16 through 23 lbs.
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