balance weight

A landlord from Chesapeake Virginia says:
I am replacing 25inch and 29inch balances and can not find a weight stamp on the balances. The series 370 appear to be correct balance. The un-tensioned spring on the 25 inch balance is 7 inch; a total length of 18.5 inch from the pin holding the block and tackle and the pin holding the end of spring. The un-tensioned spring on the 29 inch balance is 12.75inch; a total length of 26.25 inch from the pin holding the block and tackle and the pin holding the end of spring.
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Tom from SWISCO responded:
I'm afraid knowing the size of the spring doesn't tell us anything. If you have no stamps on the old balances to reference, you will need to weigh your sash on a scale and refer to the weight chart we have for both the S370-25 and S370-29.
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