Anderson Window double hung sash balancer replacement identification

A handy person from Manchester, MO says:
September 15, 2013
Hello, I need to replace a couple of my Anderson window sash balances because the strings broke. The numbers on the sash balaners are:

P90 13L 2-88 (top right sash balancer viewed from inside house)
P90 R13 2-88 (top left sash balancer viewed from inside house)

Can you please identify replacement sash balancers for these? Thanks!
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Paul from SWISCO responded:
September 19, 2013
We're having a little trouble finding the right balance for you. Could we see a few pictures of each stamp printed on the balances? Sometimes seeing how the numbers are printed is just as important as the numbers themselves.
A quick learner from Manchester, MO says:
September 23, 2013
Please see the attached pictures. It still looks like I identified the numbers correctly. They also have the "Anderson Window" stamp on them.
User submitted photos of a window balance.
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Tom from SWISCO responded:
September 24, 2013
Great, these images are perfect. I just wanted to confirm the location of these stamps. Check out our 24-13R and 24-13L.
A quick learner from Manchester, MO says:
September 24, 2013
Thank you for that information! Just to confirm, are these the right replacements:

24-13R replaces P90 R13 2-88 (top left sash balancer viewed from inside house)

and

24-13L replaces P90 13L 2-88 (top right sash balancer viewed from inside house)?

I'm a bit confused about the handedness because the "Right" sash balance is on the top left of the window and the "Left" sash balance is on the top right of the window (viewed from inside the house). I actually need to order two replacements (for two different windows) for the top right sash balance, which I believe corresponds to 24-13L.
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Tom from SWISCO responded:
September 24, 2013
Yes, 24-13R would go with the balance stamped with R13, and 24-13L would go with the balance marked with 13L.

As for the what side they go on, that's a little more tricky. If your balances worked fine before, then personally I think you should stick with what you had. There may be a reason why the original installers did it that way.
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Casey from SWISCO responded:
September 24, 2013
Hi, I just wanted to add a note...

The handing sounds correct, Andersen handing for this type of balance is as viewed from outside your home looking in.
A quick learner from Manchester, MO says:
September 24, 2013
Thank you, Tom and Donna. I suspected as much about the Andersen handing, and I verified it on another window. I've got a couple of 24-13L's on order with you. Thank you very much for your help!
Andersen Sash Balance, 13L, 12SL
Andersen Sash Balance, 13L, 12SL
24-13L
$54.20
Andersen Sash Balance, 13R, 12SR
Andersen Sash Balance, 13R, 12SR
24-13R
$54.20
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