http://chdk.wikia.com/wiki/FAQ
I haven't tried this myself, but I know a few here have yet to transfer over to the wonderful world of SLR cameras, so it might be of use to someone. Here's a firmware update for all of you Canon users with Powershots and a few others. It's a firmware extension that allows you to utilize the following functions, plus a few more.
# Shooting in RAW
# Live histogram (RGB, blended, luminance and for each RGB channel)
# Zebra mode (blinking highlights and shadows)
# DOF-calculator
# Battery indicator
# Scripts execution (exposure/focus/... bracketing, intervalometer and more)
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