Sash channel Balance
A quick learner from Denver says:
October 11, 2016
No indentifying marks on the window and nothing but bsi 2640 on the balance. I've tried submitting pictures but the form fails.
Tom from SWISCO responded:
October 13, 2016
I'm afraid I cannot identify what you have based on the stamp alone. I recommend that you look at our Channel Balance Home Page and follow the steps in order to find the Series that best matches what you have.