    # File lib/prawn/font/afm.rb, line 56
          def compute_width_of(string, options={})
            scale = (options[:size] || size) / 1000.0

            if options[:kerning]
              strings, numbers = kern(string).partition { |e| e.is_a?(String) }
              total_kerning_offset = numbers.inject(0.0) { |s,r| s + r }
              (unscaled_width_of(strings.join) - total_kerning_offset) * scale
            else
              unscaled_width_of(string) * scale
            end
          end