Measuring Spiral Balance.

Hi,

I'm preparing to order some spiral window balances.

The existing balances (some broken, some not broken) have vinyl tubes vs. aluminum. When measuring the tubes, I notice that they don't extend to the end of the spring.

I measure 35" from the top of the tube (Where it's screwed to the window) to the bottom of the tube (below that, an additional ~3/4" of the spring is exposed).

I measure *about* 36" from the top of the tube to the tip of the red bushing.

Would I order 35" or 36"?

Also, how would the operation of the window be affected if replaced a 36" balance with a 35"?

Thanks a bunch!
Craig