I can say I've never owned a scale and I still have a pretty good idea of my weight. Every time I've been to a hospital I've been within 5-10lb of my last visit. It helps that I can actually see the difference in my body if I put on or lose 10lb. I've had a few pairs of jeans for years and I just know if they're fitting a little differently, that I've probably been eating differently. Thin privilege is being able to notice minor changes in your physique after years of maintaining a recognizable standard for yourself.