def string_width(string, font_size)
      font_scale = font_size / 10.0
      string.count(Worksheet::THIN_CHARS) * font_scale
    end
def string_width(string, font_size)
      font_scale = font_size / 10.0
      string.count(Worksheet::THIN_CHARS) * font_scale
    end
Returns the width of a string according to the current style
 This is still not perfect...
  - scaling is not linear as font sizes increase