The buttons aren't too hard to reach- they're all together at the top of the box. see here http://www.nielsenkellerman.com/rowing/coxbox_new.html
. The stop/ start button is right in the center of the three so it's an easy target. To clear, you press the right button and hold- the display will count down 3, 2, 1 and the zero out. There is also a battery level indicator that shows you how charged your battery is (like on your ipod) which is nice so that you know if you need to throw a new one in before you have time to charge it.
I had it in Amsterdam with me when I was racing 2 weekends ago and it worked great.