What a moron. I wanted to draw some nice straight lines, using a permanent marker, so I selected my "architect style" 3 sided scale ruler, with lovely gradations in various scales such as 1:20, 1:50 etc. I drew my nice straight lines, even used the gradations to get them the same length. Then I saw that the marker had left some nasty  black lines in the edge of my straight edged scale ruler. I used a lens wipe to remove the permanent marker.
Unfortunately it also removed the rest of the "permanent" marks, being all the scale gradations. Now I have a triangular straight edge!  LOL.
Cheers, Bill.

  for posting this - your experience will help prevent others (i.e. me) doing the same!

Oh hec Bill, well I have a Starret 6" combination square and it is very grimy and I am at sixes and sevens what to clean it with and I do not know what to use, I shall not use chemicals as I do not need the markings to come off, but I think I will try some soapy water and see what that does, the set square is over 25 years old so to lose it with no markings on it would really upset me.

Hi Geoff, there is a good chance that your Starret is engraved and ground,( they are not the right words, but I am floundering for the correct term, but hope you know what I mean) rather than the "high quality" Chinese Rolson (mine) where the numbers are merely printed onto the ruler.   
We live and learn, eh. What interests me, is this. If the "lens cleaner" has such a damaging effect on my ruler, then what is it doing to the coating on my specs?
have a great day, Bill.