Continuing on this quest for perfect weighing:
Essentially: the same time, every day, as naked as possible.
That’s really about it.
Obviously, your level of nakedness will depend on where you are when you do it (and your level of comfort). But you want consistent circumstances; for me, that tends to be first thing in the morning, right before showering. I might switch that up to “right after I get out of bed”, because that’s the absolutely most consistent time.
The daily weighing, weekly averaging should take care of fluctuations from there.
Saturday mornings are actually kind of weird for me, because it feels like it should be a lazy weekend morning. But due to the radio show, I actually leave the house about 40 minutes earlier than I do on weekdays, so I have less time than usual. So Saturday is my exercise break day, but I’m still going to try to weigh myself.