I have just been having a prolonged argument with people at work about whether it is correct to write "three weeks notice" or "three weeks' notice". My view is that, since a week cannot possess the notice and it is not an abbreviation with an absent letter, it is incorrect to use an apostrophe. The notice, is anything, is possessed by the person to whom it is given (i.e. she gave him his notice). Merge, Purple Dragon, I see that you agree with this. Do you know of any printed source which would verify it?