What does 'ten of six' mean in regard to time?
As a non-native speaker, I consider a quarter past nine (9:15) and a quarter to nine (8:45) easy to understand. However every time I hear "a quarter of nine", I have to pause for a few seconds and make sure I get it right.
How did this expression come about? How to explain it? I googled and the answer to this question on Yahoo! might be wrong.