Step 4: replace "global " with "variable "

Original:

proc updateBoard {} {

    global cellarray possarray
    global cellchangedcolor
    global arabicmode

    for {set index 0} {$index < 81} {incr index} {
        set singlevalue [checkPossibleForOne $index]
        if {$singlevalue != 0} {
            if {!$arabicmode} {
                # convert to kanji first
                set singlevalue [toKanji $singlevalue]
            }
            set cellarray($index) $singlevalue
            .sudoku.board.cellentry$index configure \
                -bg $cellchangedcolor
        }
    }
}

Final Code:

proc ::sud::updateBoard {} {

    variable cellarray 
    variable possarray
    variable cellchangedcolor
    variable arabicmode

    for {set index 0} {$index < 81} {incr index} {
        set singlevalue [checkPossibleForOne $index]
        if {$singlevalue != 0} {
            if {!$arabicmode} {
                # convert to kanji first
                set singlevalue [toKanji $singlevalue]
            }
            set cellarray($index) $singlevalue
            .sudoku.board.cellentry$index configure \
                -bg $cellchangedcolor
        }
    }
}