I use a white board and place the singers by a number as they come in. When I add their song to the list I right click and add their number to the right of their name. That way if I have 10 or 40 singers it does not matter. I keep the numbers in order and all flows smoothly. If it is an extremely busy night and a new singer comes in late and say we are on singer number 5 out of say 35, I will make the new singer number 8.5. Whatever number a singer gets they stay with that number for the rest of the night.