Shapely?

So, Morgan owns a bathroom scale.  No big deal, I have an idea of the 15 lb range I've tended to fit lately, rarely at the edge though.  So I stepped on the scale on Tuesday (the first time in weeks) and weighed X, which is on the low end of my range. Yay! This is great for going into the holiday season.  Today I step back on and weigh x+6.  How'd that happen?