http://www.frets.com/FRETSPages/Musician/GenSetup/TrussRods/TrussRodAdj/tradj.htmlhttp://www.geocities.com/chrisdavis_1/TRUSSRODADJUSTMENT.htmlleave it alone unless you've got big problems! Even if you've got big problems, ask one of us and/or take it to a repairer.. they won't charge the earth.
It's used to set the amount of relief or "gap-under the strings",but can be vexatious and it AINT a toy.
^Chacron^ - some nuts may be cut a "Bit too wide" and accept larger gauge strings, but, a properly cut nut for 9 gauge strings will likely "pinch" 11s -because precision files should be used to cut the string slots..
-this causes ..problems,such as excess friction (ie,trem will not return to pitch) and 'storing' tension in the length from the tuner to the nut - incorrect tuning and intonation..best to get these done by repairers as well, really..can be a pig to get right.
I've just put a graphite nut on my Kramer as the cheap plastic one was cut too wide/deep and was a general pain,but, i have nut files (
http://www.stewmac.com ) and several years of ruining nuts and bending rods (jk) behind me :)
The truss rod for a Gibson should be just behind the nut,under a plate,although it's not unheard of for BOLT ON neck guitars to have the rod adjustment at the body/heel end.. got a cheapy which has this, like i say truss rod and nut adjustment are every day jobs for repairers so shouldn't cost much for them to do for you.
Accuracy,you say? hmm interesting concept..