How do you stand on a scale for the most accurate weight?

I have a digital scale and the way I stand changes the weight drastically. I don't know if it's just a sucky scale or if I am standing on it wrong are you suppose to put the weight on your heels, center of your feet or on your toes? This sounds like a really stupid but I am completely serious! Or should I go with the smallest number or the biggest. It's like 5 lbs difference.