如何在Excel中显示运行中的时钟?

I'd like to show a clock in cell A1 of Excel 2007. I'm familiar with NOW() and TODAY() but it doesn't refresh itself every 1 minute like I want it to. You know, like a running clock. I just want the current time in h:mm to be in cell A1. Is this possible?I'd like to show a clock in cell A1 of Excel 20