Determines a column on this Combo where data is stored. For example, if each row contains eight items and this property is set to 3 (three), this object stores information on the third column of the currently selected row. If its value is set to 0 (zero), this value is passed to object's ListIndex property. If its value is equal to 1 (one) or higher, indicated data is attributed to the column referring to the value specified in this property. Columns start at 1 (one).