I understand that it doesn't 'do things to a column' as such (sorry, my poor use of language there!) - I'm trying to understand what it exactly does do.

I know...

Thanks Phil, I'll give that a try when I get back in the office tomorrow. But out interest, am I right in thinking that a derived column can do...

That's really helpful. New to SSIS and hit this error and I've been scratching my head for the past half hour.

Nice one!