6
No, don't laugh... this is serious. I used to use Win-merge to detect document/script differences. Then one day my pet minor bird was looking over my shoulder and said "dat one dare" he means that one there of course. I did not know what he meant at first then as I ran my fingers over the compared document, he squaked again "dat one dare" I underlined each occurance and checked only to find he had see every single difference, even tiny marks like full stops!
The bird's got the eye!