A few things to keep in mind:
1.) Quality costs. The $29.99 Target special won't give you accurate readings. The scales at Weight Watchers cost about $1000 each. The more you pay, chances are, the better the quality, and therefore, the more accurate your results.
2.) Keeping your bathroom scale in a bathroom usually isn't the best place for it. Especially if you keep it in a full bath. (As opposed to a half one....neither one is good, but especially not a full) The moisture from shower steam can get inside of the scale and damage it. The bedroom is probably the best place to store it.
3.) Lots have said it....the scale has to be on a completely level surface, with no carpeting. The carpeting absorbs some of your body weight, and therefore gives lighter readings. (If accuracy is what you're after, keep it off the rug, but I'm so vain that I think I'll keep mine ON a rug!!!

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If you're using a bathroom scale as your tool to weigh-in, splurge and buy one of those really expensive ones. If you weigh in at a doctor's office, or a WW meeting, don't spend tons of money. Just use the cheapy ones to let you know if you're in the range you want to be. Give yourself leeway of about 4 pounds either lighter or heavier.