Broken spring in a coil balance

A quick learner from Charlotte, NC says:
My wife told me one day "the window won't stay up". Flash forward 6-8 months later, I finally looked at it. After some learning, a few youtube videos and some elbow grease I found that the spring in my coil balance had snapped.

I read in several places that I can just find the stamped number on the spring and buy a new one, but I can't find a stamp anywhere on the spring. I also read that they are rated by window weight but don't know the weight of my window. I read on how to make a rough guess but it talked about knowing if I have Single Strength Insulated Glass or Double Strength Insulated Glass and I don't know how to tell. I can say that the window is 24" wide by x 29 1/2" tall. Also, the spring is 1/2" wide.

I also took a stab at the weight by weighing myself holding the window and not, and the difference came out to 19.8 pounds.

Sooooo.....hoping for some suggestions on where to go from here :-).
User submitted a photo of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Thanks for posting. Yes, if the window cannot stay up then the problem is likely the balance. Based on your pivot shoe, which resembles our 15-180, I would recommend our Series 190 coil spring. The best way to match up which Series 190 spring you have is to reference the number printed on your current springs. It should be near the screw hole. I think the S190-540 might be what you have, since four of these can carry a sash weight of 20 pounds.
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