It probably is the scales but could be just weight fluctuation; I read somewhere a person can vary up to 5 pounds in a day!So I picked up a digital scale for home use. It seems quite certain that I'm down to 160 lbs, even though my last weigh in at work showed me at 164. So either I lost 4 lbs in 9 days (unlikely), or the two scales don't match up (more likely).
I'll have to remember at some point in the near future to weigh myself at home and at work within an hour or so of each other, just to see how the two scales compare. Our scale at work isn't available this week, though, because it's locked in the office of the person running the contest, who is on vacation (which is why we're skipping two weeks' worth of weigh ins).