Speaker Positioning

My oppinion on this is to get it close but don’t loose sleep over 1/8 of an inch.  I also think that sometimes its better to not have them at the same exact distancE from the walls because of frequencies cancelling each other out.  Also, your room is probably not perfectly square.  I like to do what MC says but then use a string japed to where your head is then pull the string tight to one tweeter.  Hold that position on the string now walk over to the other speaker and make it the same distance.  
Distance to speakers and equal angles to the speakers is more important than equal distance to walls.

Shoot, speakers are going to have sliggt differences between the drivers and crossover components.

I’ve been using Sonarworks reference 4 correction software and my speakers measured slightly different between the 2 channels.  I was within + or - 3 db the whole range but with correction on, the image is perfectly centered and the frequency is flatter.  Im not certain the cost sonically speaking though of using this program.  A bit too early to tell if its something I will use all the time, part of the time or none.

Thanks gents.   By “dynamic” I was referring to physical location determined by more than just a tape measure,  Sonic measurements are of little value IMO unless you know the corresponding measurements for your left/right ear.  Once again and as anticipated, the ears have it!
I do appreciate everyone’s responses. 

I found a tape measure easiest to measure against room boundaries while making REW measurements at 4" intervals. When I was done with REW, I used a laser against a paper target at the listening position to mirror the speakers' distance to the listening position, and toe-in.
  

Well when you get to end of the setup, what else matters.. Still have to listen.

I understand difference in ear balance vs measured balance, vs SPL balance  (left and right speaker matching). It does vary quite a bit actually.
Depends on who made the stuff or if they even care..

ROOMS forget about it... no two are the same.. Anything goes..

To thine own room be true.....Know your room....:-)

Regards

Bosch laser measure, inexpensive model.  You can check the exact distance between you and the two speakers, and you don't need someone to hold the other end of the tape measure.