Canon MARK IV User Manual (en)

Custom Function Settings
C.Fn IV -4     Assign SET button
You can assign a frequently-used function to <0>. Press <0> when the 
camera is shooting-ready.
0: Normal (disabled)
1: White balance
While looking at the rear LCD panel, you can change the white balance.
2: Image size
While looking at the rear LCD panel, you can change the card and 
image size.
3: ISO speed
While looking at the top LCD panel or in the viewfinder, you can change 
the ISO speed.
4: Picture Style
The Picture Style screen will appear.
5: Record func. + media/folder
The [5 Record func+media/folder sel.] menu will appear.
6: Menu display
Assigns the same function as the <M> button.
7: Image playback
Assigns the same function as the <x> button.
C.Fn IV -5     Tv/Av setting for Manual exposure
0: Tv=6/Av=5
1: Tv=5/Av=6
Convenient when you use studio flash and frequently change the 
Also, when you use AEB in the manual exposure mode, the shutter 
speed can stay fixed while only the aperture is shifted for AEB. The 
shutter speed can also be set by pressing the <O> button and turning 
the <6/5> dial.
If the camera has been set to enable Live View shooting (p.126) or movie 
shooting (p.142), the Live View or movie shooting will override all of the 
above settings 1 to 7.