That's what I do. I pick one time each week, and the same conditions. Oh, yes, you can fluxuate that much. I fluxuated 5 pounds over the course of a day. I do first in the morning, preshower, post bathroom. I picked Thursday just because of the fact I wake up at the same time during the week cause of work. The difference over a week will show you a more stable view of your weightloss.