In Chess You Cannot Afford to Be Off by 5 Degrees
Here is one of those dreaded word (story) math problems:
PROBLEM: You and a friend set out walking 100 miles through the snow. You had an hour head start. You walk the same speed for the entire distance. You both had compasses and were told to head due north. Because of the fresh snow and wind, your friend cannot see any of your footprints. Unknown to either of you, his compass is off by 5° (in other words, heading due north he will end up 5° towards the east). When he has finished his 100 mile journey (an hour later than you did), how far from you will he be?
ANSWER: He will be tired and over 4 miles from you!
RELEVANCE: In chess, your calculations must be exact or your game will be walking home. In a game earlier this evening, my opponent (cgatten) miscalculated by one move. In the process he lost his queen and the game (see http://www.chess.com/echess/game.html?id=2267841).
Don't rush your calculations. If it is not a timed game and it is an important move, go over it several times. Make sure you double check how your opponent can respond. This is where I have seen lots of calculations go wrong! They only see one way the opponent can respond, and when the opponent moves a different piece or a different combination of moves, their calculations fall apart! Don't risk being off by 5 degrees in your next game!