I believe this is exactly what it mean to be a slave to the scale - and every article I read always says don't do that. Not being preachy but seeing different numbers on the scale could be the way your body is positioned or if you're leaning back or something. It could be that you just drank a glass of water or that your hormones are helping you retain water. Remember its not just how much you weigh but how healthy you are overall. As long as you see a consistent loss over the course of a month or two it should be fine.
So in answer to your question I weigh myself once a week and take it at face value. NOw that you've suggested this I might think about it though