RL Baffling: 2 weeks ago, weight at GP was XX2, last friday at U of M it was 20 lbs less, and today at GP it was back to XX2. So....someone's scale is CLEARLY broken, but WHOSE?

GP has a new scale as of today and was recently calibrated

I mean, it must be tht someone's scale is off, bc it seems very unlikely that I lost and then regained 20 lbs in a period of 2 weeks, and then 4 days....right?

U of M had me stand on a scale that is clearly meant to roll a wheelchair on, so I wonder if it tared for however much the wheelchairs weighed