I try to add it all up as I go along, but get extremely annoyed by people who add up their scores
OUT LOUD 
next to me when I'm adding, as it's extremely distracting, and usually leads to me making mistakes...
So, a plea to all those 'sum-as-you-go-along' people; add it up
IN YOUR HEAD, or UNDER YOUR BREATH and not out loud! Your target partners will appreciate it!