I remember a highly entertaining article in an electronics magazine some years ago about those green pens for marking around the edge of CDs to mumble mumble bullshit better sound. The reviewer figured that if he put the green ink on half of a CD, he'd be able to detect a modulation based on the disc's rotation speed, since it would be working half the time.

He could detect nothing. Absolutely nothing. And he worked with professional audio for a living! :-D

The manufactures of said pen were not amused, but he wouldn't retract his article.

Wade.