def get_bits_for(column_name, field)
      return nil if self[column_name].nil?
      only = self.class.only_mask_for column_name, field
      inc = self.class.increment_mask_for column_name, field
      (self[column_name] & only)/inc
    end
def get_bits_for(column_name, field)
      return nil if self[column_name].nil?
      only = self.class.only_mask_for column_name, field
      inc = self.class.increment_mask_for column_name, field
      (self[column_name] & only)/inc
    end
:nodoc: