Canon EOS-5D Instruction Manual page 87

Shutter Speed Display
The shutter speeds from "8000" to "4" indicate the denominator of the
fractional shutter speed. For example, "125" indicates 1/125 sec. Also, "0"6"
indicates 0.6 sec. and "15"" is 15 sec.
If the maximum aperture blinks, it indicates
underexposure. Turn the <6> dial to set a slower
shutter speed until the aperture value stops blinking.
If the minimum aperture blinks, it indicates
overexposure. Turn the <6> dial to set a faster shutter
speed until the aperture value stops blinking or lower
the ISO speed.
s Shutter-Priority AE
87