I seem to remember that AVS forums has a forum, or at least lots of postings re the SPL meters.

THEY ARE NOT LINEAR !!! I think the adjs might be up to 10 db depending on frequency.

Try a google search to find the calibration adjustment settings for SPL meters - correction tables (or other equiv term.)

Here are a couple places to start, there are tons of threads, if you find a concise and easy one to use, pls post it:

http://archive2.avsforum.com/avs-vb/archive/index.php/t-636795.html

http://www.avsforum.com/avs-vb/showthread.php?t=505236

Have fun-but in the end, trust your ears. Remember, everyone's hearing is different-ask an audiologist.