I usually weigh myself first thing in the AM. But our scale isn't the greatest, so I'll weigh myself at the gym, which has a doctor's scale. Usually, that's later in the day, so I take that into account. Also I don't tend to weigh myself just before or during my period. I wait until a couple of days after it ends.
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You can catch more flies with honey than with vinegar. That's great...if you want to attract vermin.