Clock wipe effect

I need to do a “clock wipe” effect for a client’s logo and I can’t seem to find any tutorials on this. A portion of their logo is circular, so they want it to be revealed in a fashion where it becomes visible in a clockwise fashion. Someone told me they saw a tutorial for this in a flash book, but couldn’t remember which one it was. If anyone knows of any tutorials or has any sample files, I’d greatly appreciate it. Thanks!