Speaker Calibration Disparity

I have calibrated my Sherwood using an Spl meter with test tones. You know, 00db, to 75 on the meter ya da ya da...

Why is it when I used the THX test tones on my Attack of the Clones DVD the calibration settings on my speakers were totally different? I used the same SPL meter, same settings and everything. How am I supposed to know which is correct?

I've always been wary of the THX Optimode tests, ever since they first appeared on some DVD's with the rather odd qualifier that they were customized for the movie they were attached to. Instead, I've generally relied on my receiver or pre/pro's internal test tones, although I've also used Video Essentials a couple of times. Either of those methods would be a better way to calibrate a system for general use than the Optimode test tones. Here are a few links discussing THX Optimization and THX Optimode:
SMR Article
THX info page
TechnoFILE article
The first link is of particular value in this case, as it discusses the limitations in Optimode. It's best summed up in the following quote:

Thanks Gonk. I do have a Digital Video Essentials on the way. My Sherwood also has a calibration feature that adjusts itself for room acoustics, etc. but for some reason it wants to set all my speakers to Large so I just do the SPL.

Okay how about this one. Should I calibrate the test tones on my DVD player or just leave them alone and let the Sherwood calibration handle it?

i would let the sherwood do it.

Thanks...I actually compared them both last night and they are right on the money with each other.