Paul from SWISCO responded:
December 5, 2016
The option indicates spring strength. You can usually use the stamp printed on your metal channel as reference, but yours appears to be different than any of the options we have. That probably means your balance was just made by a different manufacturer. I recommend weighing your sash on a scale and referring to the chart shown on the S775-18 store page, that will tell you what will work best.
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