Found two different size balances in one window

A home owner from medford, MA says:
We have been ordering your 29 inch spiral balances (S600-29) to replace the upstairs window balances at my daughters home.

Recently on a downstairs window that we were working on we found two different spiral balances(one on each side), one was 30 inches long and the other was 31 inches long!! Which size should we order for this window?
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Mike from SWISCO responded:
Good Afternoon,

It sounds like someone replaced the balances in that window (at least one of the balances) and they did not have the correct size replacement.

Take a look at the two balances. Can you tell by looking at them which one looks to be the older original balance? Are both balances mounted at the same position near the top of the window frame?

What is the size of the visible glass of your window sash?
A quick learner from medford, MA says:
Cant tell which one is the original balance. Both were mounted in the same position. I forgot to mention that we took out the two balances(30 and 31 in.)and replaced them with two 29 in. balances that we had ordered before from you. But then the bottom sash would not close all the way, which is why I contacted you. It wouldnt go closer than about 1 inch from the window sill. So we know that the combined 30 and 31 in.balances at least allowed the window to close.

The visible glass on the top window frame is 27 1/2 in.vertical(entire window frame is 31 in. vertical) and the visible glass on the bottom window frame is 27 3/4 in. vertical(entire frame 31 3/8)

Should we order 31 in. balances?
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Paul from SWISCO responded:
Yes, the 31" balance will be the best fit.
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