indexing your nock with a spine tester, does it make a lot of difference in accuracy

If with wood, yes. Assuming you're speaking of spine accuracy. Shooting accuracy? yes as well. Wood spine reading will be different if your grain is not perpendicular with the spine mechanism. (Up/down) Pull against the growth ring grain.

It does make a difference  with carbon as well. Maybe not as drastic as wood but still varies a few lbs based on orientation  of how the shaft lays on the tester

that said

wich spine tester do you recommend

forgot to mentioned I use mostly alluminium

Didn't know that about carbon, warden415. Have you  ever seen a larger variance than just a couple pounds?

http://www.3riversarchery.com/ace+spin-spine+tester_i5900-1_baseitem.html

I use a homemade one.

I use the Ace Spin-Spine that Bud linked above, but the others work fine too.  Whichever you use, make sure to zero it before each reading; it make a difference.

FWIW, aluminum is very consistent so don't expect to see much difference in it.  Wood and carbon is another story.

I built a real simple homemade one.  There was an article in TBM a few months back.

Bud B I have not seen huge variances  but 5 lb is not uncommon. . I have read where others have seen greater variances. I havnt had my tester all tgat long so I havnt been able  to. Test alot of different brands of carbon.

I use this one

I have been wanting to build this for several years and now have had the time to do it.  It is all electronic and both weighs the shaft and spines it.

http://youtu.be/LCbjCFox8BQ

Each support has a load cell that works just like your grain scale.  The stepper motor linear actuator applies force to the arrow until 2 pounds is reached. The deflection required to reach that force is known so it is simple to calculate the spine.

There is no zeroing required because the microcomputer takes care of that for you.  Just place the arrow shaft and push the button.  It takes about 5 seconds to have the result in weight and spine.

It is very accurate and repeatable.

I never notice over a pound or two difference in wood arrows but it may be because I don't spine test shafts in the lighter spine ranges.

The lighter the bow is is more finnicky it is to match your shafts. Every archer who is not spine matching his or her arrow shafts is giving up accuracy and forgiveness, especially on bows under 60#s.