Panel 1: A while later, we find ourselves in the kitchen watching Mike telling John that he should get rid of the bathroom scales because they're incorrect. This tells me that he's got Lynn's lack of understanding about how the world works because damned near everyone I know understands that a scale that's off balance can be adjusted.
Panel 2: As he reaches into the fridge, he tells John that he got weighed by the doctor today and the scales are off by five pounds. This tells me that we're looking at Lynn telling Rod to do something only for him to tell her that all she needs to do is to flip the scale over and adjust the silly thing.
Panel 3: Since showing her how to adjust it worked as well as showing her how a CD case will, John merely asks if it's five pounds too much or too little. Mike says "Lower"
Panel 4: As John drinks his coffee, he thought-bubbles that they'll keep the scales.
Summary: As I keep saying, this should be Mike telling John to adjust the little wheel so that the scales are right but Lynn doesn't know about that whell and, when shown, goes right on not knowing because she's too stubborn to be taught things.