Like Stuart said, you'll need to specify a fixed size for the cell. Since the font you are using to display your clock is proportional (each character only takes up as much space as it needs, as opposed to a fixed-width font where every character takes the same amount of space, like this), the width necessary to display it will change every time the clock changes. You could use a proportional font (Courier New is the most common), or set the cell to a specific width so it never uses less space. It's easy to do, just set the width value of the cell. The hard part is trying to figure out how wide it needs to be. You can take a screenshot then use an image processing application to measure how wide it needs to be, or take some educated guesses and try them out until one works for you.