Maidir leis an mbreiseán seo
On the ruler, current position and wrapped position are highlighted. Scales are mostly exact on plain text mail with monospace fonts. However, if lines are wrapped by words or URI strings, they are not exact. HTML mail and proportional fonts also confuse the ruler.
Yes, this is a clone of "Rulerrrrr" ( http://sandbox.minutedesign.com/extensions/ ).