#!/usr/bin/wish
wm withdraw .
set Xw [winfo screenwidth .]
set Xh [winfo screenheight .]
wm overrideredirect . 1
pack [label .l -text "05"  \
    -font "Helvetica 24"] \
    -padx 30m -pady 30m
# NB - Use gfontsel or xfontsel to pick a better font.
wm deiconify .
update; # forces packing
set Ww [winfo width .]; set Wh [winfo height .];# get packed size
wm geometry . [format +%d+%d [expr ($Xw-$Ww)/2] [expr ($Xh-$Wh)/2]]
update; # centered box 
for {set i 4} {$i>=0} {set i [expr $i-1]} {
  .l configure -text [format %.2d $i]
  after 1000
  update
}
exec xset dpms force standby
exit