weigh ins

I know this topic has been covered before but I wanted a few opinions on my issue. I weigh myself on Sundays as my official weigh in day and I put that number into MFP. On most weeks Monday morning I weigh a pound or even two less than on Sunday. For example this week Sunday I weighed 168.9 and Monday I weighed 167.5. Should I change the day I weigh in or leave it be because it doesn't affect the overall trend of the numbers moving down? It’s not really a big deal but it’s kind of bothering me. That silly scale is being tricky.