[expensive_hobby]

Originally Posted by cyclohexane

I believe you are correct for partial (9%) and center-weighted average meter modes.

I haven't found an answer for what the meter is looking for in evaluative; the Canon white paper on the XT didn't turn up anything conclusive. Hopefully someone with more knowledge can chime in as to whether Canon's evaluative metering factors in color information or not.

I never thought of googling it, but you inspired me to! Here's what I have found from Canon's site- Canon Technology:

Canon developed a 21-zone metering sensor to accommodate 45-point area AF. Using a newly developed algorithm, this metering system performs high-speed calculations of output from 21 zone sensors and AF information, and adjusts exposure instantly.
This configuration enables the camera to make compensations appropriate to shooting conditions and maintain exposure stability. The system also incorporates an average metering element that factors in periphery conditions, providing accurate exposure even when the composition changes slightly, or when the subject covers multiple metering points.

I'm thinking a couple of things here. Primarily even though there's a picture with the text, and I know it's using the AF points, I still don't know how it's deriving the settings as it takes in the "scene".

So evaluative metering is probably best for snapshots? And by using the partial and center-weighted metering, because the camera is aiming it's settings for middle gray I should have an easier time concluding how the exposure is effecting the image?

Edited: That description was for slr cameras, not digital. I'm assuming it's semi-safe to say it's almost parallel to how the digital cameras work.