Canon EOS 5D Mark III Instruction Manual (en)

 Custom Function SettingsN
C.Fn2: Disp./Operation
Warnings z in viewfinder
When any of the following functions are set, the <
h> icon can be 
displayed on the viewfinder’s bottom right (p.23).
Select the function for which you want the warning icon to appear, press 
0> to append a <X>, then select [OK].
When monochrome V is set
If the Picture Style is set to [Monochrome] (p.133), the warning icon will 
When WB is corrected
If white balance correction (p.142) is set, the warning icon will appear.
When one-touch image quality is set
If you change the image-recording quality with the one-touch image 
quality function (p.334), the warning icon will appear.
When ISO expansion is used
If the ISO speed is set manually to L (50), H1 (51200), or H2 (102400) 
(p.127), the warning icon will appear.
When spot metering is set
If the metering mode is set to [Spot metering] (p.170), the warning icon 
will appear.
LV shooting area display
When the aspect ratio for Live View shooting is set to [4:3], [16:9], or [1:1
(p.206), you can set the display method for the shooting area.