"With the older EOS-1D series cameras, the basic shooting operation logic consisted of
holding down a button and turning the Main Dial or Quick Control Dial to select a setting.
However, with the EOS-1D Mark III, when you press a button, it remains active for a while
so you can let it go and then turn a dial to set something. Also, the three buttons on the
top left of the camera accept double pressing. You can therefore set something (except
AEB) with just one button."