Invoking the CHDK menu is almost as simple as invoking the native menu. Switch to the <Alt> mode by pressing the ALT button, and then press the MENU button. You can exit the menu by pressing the MENU button again or by pressing the ALT button, which will also leave <Alt> mode and return to normal mode. [...]

We have already mentioned the ALT key. Use it to switch the camera into <Alt> mode (or CHDK mode) where all CHDK menus and scripts are accessible. Note that while in <Alt> mode, none of the keys (including the shutter release) work in the traditional way. To return to normal operation, you must leave <Alt> mode. This is done with another [...]