I have used the Velodyne SMS-1 parametric equalizer and found that moving the mike (pickup) around does make a significant difference in the readings. I am sure that an SPL meter is even less sensitive. When it comes down to the nitty gritty I think Curegeorg is right, it's best to use the end results in determining what sounds right via the ear. The mechanical method, although we all want to get it as close as possible, is a second guess in comparison with the EAR, opps, I mean END results.