Whenever I feel like it (anywhere from once a day to whenever I go to the bathroom), but it does typically end up just being after I pee, since that's when I'm in the bathroom anyway. I... don't take any clothes off, except for shoes. I'm happy as long as the needle is between 165 and 170.
But that's actually kind of a good point. I got a 10 dollar ANALOG scale from Walmart and the numbers are so small that I can't read them without taking a picture of it with my camera while standing on it and zooming in afterwards. So... I only have an official weigh-in once every 2 weeks, when I do that. That's the only time I change my weight here. Other than that it's like a sort of... eye-balling it. Like oh I'm still around 165 (not sure of the exact number)... that's good.
I'm not going to SEE things like that I'm up .2 pounds, so I never even have to worry about that kind of thing bothering me.

And I ONLY weighed once every 2 weeks PERIOD until I was actually happy with my weight. Because before then if I WAS up a few pounds I'd get depressed, but now it doesn't bother me, as long as I'm still in the 160's, since I'm happy here.
So basically... GO ANALOG SCALE!