The Main Dial is located just behind the shutter button on the camera-right side. You will use this wheel to change Focus Points, make Exposure Compensation adjustments, change ISO, and to control many more functions (FIG 4.3).
EOS-1 bodies have an extra Main Dial (with its own on/off switch), along with an additional FEL button and shutter release, located under the camera’s right side grip. Called the Vertical Grip Dial, this extra dial allows the photographer to control everything while holding the camera in a vertical position. If you’ve never had a camera with this feature it may take a little getting used to, but once you do you’ll wonder how you ever got by without it (FIG 4.4).