How to show a clock at top of UITableView that constantly updates?

My users enter time information and I need to show local and UTC clocks (digital) at the top of the screen for them to reference. How can I do this and have it update every second 开发者_开发技巧or few seconds? I can add a header view or text to a section header/footer but I'm not sure how to refresh it.

Thank you.

Use an NSTimer as suggested in the question's tags - see post.